Radio frequency microelectromechanical systems (MEMS) devices on low-temperature co-fired ceramic (LTCC) substrates

ABSTRACT

A phased-array antenna system and other types of radio frequency (RF) devices and systems using microelectromechanical switches (“MEMS”) and low-temperature co-fired ceramic (“LTCC”) technology and a method of fabricating such phased-array antenna system and other types of radio frequency (RF) devices are disclosed. Each antenna or other type of device includes at least two multilayer ceramic modules and a MEMS device fabricated on one of the modules. Once fabrication of the MEMS device is completed, the two ceramic modules are bonded together, hermetically sealing the MEMS device, as well as allowing electrical connections between all device layers. The bottom ceramic module has also cavities at the backside for mounting integrated circuits. The internal layers are formed using conducting, resistive and high-k dielectric pastes available in standard LTCC fabrication and low-loss dielectric LTCC tape materials.

FIELD OF THE INVENTION

[0001] The present invention relates to Radio Frequency (RF)Micro-electro-mechanical systems (MEMS) and devices that are fabricatedon or within Low-Temperature Co-Fired Ceramic (“LTCC”) substrates. Thepresent invention also relates to a method of fabricating, integratingand packaging such MEMS RF devices and systems using MEMS and LTCCtechnologies.

BACKGROUND OF THE INVENTION

[0002] Microelectromechanical systems (MEMS) have been shown to beuseful for a variety of consumer, industrial and military applications.Most MEMS devices are fabricated on semiconductor substrates (e.g.,silicon, Gallium Arsenide, Silicon-On-Insulator, etc.) using standardIntegrated Circuit (IC) processes in combination with specializedmicromachining processes. Collectively these manufacturing technologiesare frequently called microfabrication processes.

[0003] Conventional MEMS processes which are performed on silicon orother semiconductor substrates can lower the cost of products, but notto the extent required for many consumer or industrial applications.Typically, MEMS devices are batch fabricated, either as discretecomponents or directly on or within integrated circuits (“IC”) as a partof a merged MEMS-IC process. Although both approaches can potentiallylower cost somewhat, the reduction is not sufficient for manyapplications. Even if a sufficiently low cost process for thefabrication a MEMS device can be achieved, the manufacturing of MEMSdevices can incur significant additional costs associated with packagingand integration, resulting in an expensive overall system or productcost. The fabrication of MEMS devices directly on or within integratedcircuits (“integrated MEMS”) requires expensive process development aswell as some compromises in device performance. Both approaches are alsolimited by total processing area, and the resultant gains from theseapproaches are modest at best. Consequently, one of the key limitationsof MEMS technology has been the cost of manufacturing MEMS devices andsystems using semiconductor substrates and microfabrication processtechnologies. Another limitation relates to the high cost associatedwith packaging these devices and systems. Yet another limitation relatesto the cost and difficulty of realizing systems wherein MEMS andmicroelectronics are combined into modules or integrated together toform functional systems. Therefore, there is a tremendous need for morefunctional and cost-effective fabrication, packaging and integrationtechniques for implementation of MEMS-based RF devices.

[0004] Recently there has been a large interest in making MEMS RadioFrequency (RF) devices and systems for a variety of high volumecommunication applications. Although MEMS-based RF components andsystems have been demonstrated, all have been realized on traditionalsemiconductor materials, primarily silicon wafers. While this approachworks for the demonstration of a device, it has several severedisadvantages for the performance and potential commercialization of RFand microwave devices. First, the dielectric losses of the siliconsubstrate are very high at frequencies above 1 GHz. Second, the cost ofsilicon substrates and processes used to fabricate MEMS RF devices onthese substrates are too high compared to existing technologies. Third,the packaging costs of silicon and other semiconductor material basedMEMS devices are very high, particularly for devices that must operateat high frequencies and under extreme environmental conditions.

[0005] While the losses of the silicon substrate can be reducedappreciably by selectively removing the silicon from under the activedevices and the associated signal paths using an isotropic etchant, suchas Xenon Diflouride (XeF2), this is an expensive process and one that isnot readily compatible with the fabrication of active MEMS devices.Consequently, the resultant manufacturing yield will be low and the costwill increase appreciably. Other semiconductor substrates having lowerdielectric losses can be employed for the fabrication of MEMS devices,such as Gallium Arsenide (GaAs), resulting in high performance devices.However, the cost of these materials and the costs to fabricate deviceson these materials are typically two orders of magnitude higher thaneven silicon wafers and processes. Consequently, the resultant device orsystem cost will be far too high for many consumer or industrialapplications. Furthermore, any semiconductor based MEMS device willrequire a separate packaging technology that will need to bespecifically developed to meet the demanding requirements of acommercial product. Packaging techniques that can meet the requiredspecifications and simultaneously provide a sufficiently low cost havenot been readily available in the past.

[0006] Nevertheless, there is enormous opportunity for MEMS technologyin the application of RF and microwave devices and systems. If the costand performance goals can be met, the potential market sizes for thesedevices will be enormous. However, in order to exploit this opportunity,there is a need for a new low-cost material that has low dielectriclosses at high frequencies and onto which MEMS devices can besuccessfully fabricated with high yield. Furthermore, there is a needfor the capability to suitably and inexpensively integrate these MEMSdevices with other MEMS device and components to form functionalsystems. There is also a need to suitably and inexpensively package MEMSdevices and systems. It is useful to elaborate in some detail aboutspecific RF and microwave MEMS devices and systems that can greatlybenefit from fabrication, packaging and integration that can beperformed on a low-cost low dielectric loss material.

[0007] MEMS Radio Frequency (RF) switches have been shown to have verylow dielectric losses at very high frequencies, if fabricated onspecialized substrate materials such as GaAs. Compared to traditionalactive microwave switches (based on active components such astransistors or diodes), the quality factors (where the quality factor isgiven by 1/R_(on) C_(off), where R_(on) is the resistance of the switchin the ON-state and C_(off) is the OFF-state capacitance of the switch)of these MEMS RF switches are very high. Therefore, MEMS RF switchcomponents have the potential for use in many types of applications.However, these devices have been limited due to the extremely high costof fabricating and packaging the MEMS switches on Gallium-Arsenidesubstrates.

[0008] An important application of MEMS switches is as phase-shifters inphased-array antennas. Traditionally, phase-shifters for phased-arrayantennas have been implemented using active electronic components (e.g.,transistors, diodes, etc.) made from exotic and expensive materials suchas Gallium-Arsenide (GaAs). Typically, even at high volume production,GaAs-based active phase-shifters can cost more than 100 times tofabricate and are more than twice as lossy as MEMS phase-shifters. As aresult, phase-shifters are the main cost driver in phased-arrayantennas. If active electronic GaAs phase-shifters are employed, about45% of the overall cost of a receiver antenna system can be attributedto the phase-shifters alone. This is attributed to the high fabricationcost for such devices and the additional cost associated with theamplification and thermal management required by their high losses attheir operational frequencies. Consequently, due to the high cost,active electronic GaAs-based phase-shifters have been limited to use inmilitary array antennas.

[0009] For similar reasons, a variety of other-MEMS RF components andsystems, including: electronically-tunable variable capacitors,closed-loop controlled variable capacitors, tunable inductors, tunableLC filters, tunable LC networks, reconfigurable RF antennas, phasedarray antennas, as well as combinations of the above MEMS devices andsystems, would greatly benefit from the ability to be fabricated on alow-cost, low dielectric loss material. Furthermore, these devices andsystems would also benefit from low-cost and high performance approachfor packaging and integration.

[0010] Recent developments in Low Temperature Co-Fired Ceramic (LTCC)processing, combined with the recent availability of new high-qualityLTCC substrate materials having low dielectric losses at highfrequencies, have made it possible to fabricate, integrate and packageRF MEMS devices and systems with high performance and at low costs.

[0011] Direct fabrication of MEMS RF components onto LTCC substrates iskey to reducing the cost of these systems, while simultaneouslyachieving high functional performance. The use of LTCC substrates andprocessing techniques to integrate and/or package MEMS RF devices alsoprovides many advantages. The cost to attempt to integrate differenttypes of MEMS RF devices together or with microelectronics is enormous.This is because the processing steps used to fabricated the mergeddevices or systems greatly influence material properties and resultantdevice performance. Using LTCC as a substrate material greatlysimplifies and lowers the cost of integration.

[0012] With respect to packaging, it is frequently the case that thecost of packaging MEMS devices is more than the cost of the MEMS deviceitself. This is because the package must be specifically designed andmanufactured for each individual MEMS device type. Furthermore, thepackage must protect the MEMS device from the environment, butsimultaneously allow the MEMS device to interact with the environment.The use of LTCC as a substrate material that can provide electricalconnections through layers, as well as methods to make MEMS directly onthe LTCC material, and methods to affixed semiconductor substrates withhigh quality electrical connections to the activated components, whilealso providing suitable packaging protection, and at low cost, is asignificant improvement in MEMS technology.

[0013] The present invention, which uses MEMS RF devices fabricated on aLTCC substrate, allows the cost and difficulty of realizing a system tobe dramatically reduced so that MEMS RF devices can be more broadly usedfor consumer and industrial applications. The present invention, whichuses an LTCC substrate with electrical connections across or throughmultiple layers of the LTCC substrate, and when bonded or affixed toMEMS on LTCC substrates or other substrates such as semiconductor ICs,enables the device or system to be integrated and packaged with asignificant reduction in cost so that products based on MEMS technologycan be used more broadly for consumer and industrial applications.

[0014] The present invention, which uses MEMS RF switches fabricated onan LTCC substrate, allows the cost of MEMS RF switches to bedramatically reduced while maintaining excellent RF performance, so thatthey can be used more broadly for mobile wireless communication systems,including broadband satellite communications and broadband cellularcommunications, and thereby be available for use by a wide consumerbase.

[0015] The present invention, which uses any single or combination ofMEMS components, including: electronically-tunable variable capacitors,closed-loop controlled variable capacitors, tunable inductors, tunableLC filters, tunable LC networks, fabricated on an LTCC substrate, allowsthe cost of MEMS devices to be dramatically reduced while simultaneouslyachieving high performance and functionality so that these devices andsystems can be more broadly used for mobile wireless communicationsystems, broadband satellite communications or broadband cellularcommunications, and thereby be available for use by a wide consumerbase.

[0016] The present invention, which uses MEMS RF switches and/or phaseshifters fabricated on an LTCC substrate, allows the cost ofphased-array antennas to be dramatically reduced so that phased-arrayantennas can be more broadly used for mobile wireless communicationsystems, including broadband satellite communications and broadbandcellular communications, and thereby be available for use by a wideconsumer base.

[0017] Furthermore, the present invention also enables the fabricationand packaging of other micromechanical and microelectronic components,either discrete or integrated, onto substrate materials which havehigh-performance characteristics at elevated operational frequencies andlow-cost.

SUMMARY OF THE INVENTION

[0018] An object of the present invention is to provide integrated MEMSRF devices, RF switches, and phase shifters fabricated on and/orpackaged within low-cost Low-Temperature Co-Fired Ceramic (LTCC)substrates.

[0019] Another object of the present invention is to provide integratedand packaged MEMS tunable inductors; electronically tunable variableinductors; closed-loop controlled electronically tunable variableinductors; RF switches; electronically-controllable phase-shifters,variable capacitors; electronically tunable variable capacitors;closed-loop controlled electronically tunable variable capacitors;fabricated on and/or packaged with low-cost LTCC substrates.

[0020] A further object of the present invention is to provide anintegrated, low-cost and highly functional, high-performance, high-gainphased-array antenna using MEMS phase-shifters and other microfabricatedelectrical and microwave components combined with LTCC substrates.

[0021] Another object of the present invention is to provide a methodfor fabricating phased-array antenna modules that can be subsequentlytiled together with a number of indentical antenna modules to form anentire phased-array antenna system.

[0022] Another object of the present invention is to provide an entireintegrated, highly-functional, high-gain phased-array antenna systemcomposed of micromechanical, microelectronic and microwave components ona large low-cost and low-dielectric loss LTCC substrate material.

[0023] Yet another object of the present invention is to provide aprocess for manufacturing high-performance and high quality MEMS devicesand other electronic and microwave components on LTCC substratematerials.

[0024] Another object of the present invention is to provide a processfor manufacturing high-performance and high quality MEMS devices andother electronic and microwave components onto multiply layered LTCCsubstrate materials enabling efficient electrical connection between theconduction lines and components on individual layers.

[0025] Another object of the present invention is to reduce themanufacturing cost of high-gain phased-array antennas.

[0026] A further object of the present invention is to provide a methodof efficiently integrating and packaging MEMS devices and otherfunctional components, such as microelectronic and microwave devicesincluding: MEMS tunable inductors; electronically tunable variableinductors; closed-loop controlled electronically tunable variableinductors; electronically-controllable phase-shifters; RF switches;variable capacitors; electronically tunable variable capacitors;closed-loop controlled electronically tunable variable capacitors;within suitably patterned and adjoined multiply-layered LTCC substrates.

[0027] A further object of the present invention is to provide a methodof efficiently packaging MEMS device in LTCC modules on which otherintegrated circuits can be mounted to form the phased-array antenna ofthe present invention.

[0028] Yet another object of the present invention is to provide a verylow cost and effective means of batch fabricating individual discrete orintegrated MEMS, microelectronic, and microwave components such as MEMStunable inductors; electronically tunable variable inductors;closed-loop controlled electronically tunable variable inductors;electronically-controllable phase-shifters, RF switches, variablecapacitors; electronically tunable variable capacitors; closed-loopcontrolled electronically tunable variable capacitors; on LTCC substratematerials as well as providing a packages for these components fromsuitably patterned and adjoined multiply-layered LTCC substrates.

[0029] Yet another object of the present invention is to provide verycost effective packaging of MEMS devices in LTCC modules forapplications other than array antennas.

[0030] The present invention is directed to the embodiment of MEMSdevices onto or within LTCC substrates and the embodiment of discreteMEMS RF, electronic, and microwave components onto LTCC substrates.

[0031] The present invention is also directed to an integrated, low-costand highly functional, high-gain MEMS-based phased-array antenna thatcan be tiled together with a number of antenna modules to form an entirephased-array antenna system and that can be made from suitably adjoininga multiplicity of large LTCC substrate materials. The present inventionis also directed to an improved method of manufacturing the MEMS-basedLTCC antenna and other devices that use MEMS and LTCC technology and tothe packaging of discrete MEMS, electronic, and microwave componentswithin suitably patterned and adjoined multiply layered LTCC substrates.

[0032] The device or system of the present invention is a multi-layeredstructure, which contains a number of passive and active elements, someof which are MEMS devices, which are preferably fabricated onto suitablypatterned and adjoined multiple layered stack of LTCC substrates.

[0033] In yet another embodiment of the present invention, discreteMEMS, microelectronic and microwave components, such as MEMS tunableinductors; electronically tunable variable inductors; closed-loopcontrolled electronically tunable variable inductors;electronically-controllable phase-shifters; RF switches; variablecapacitors; electronically tunable variable capacitors; closed-loopcontrolled electronically tunable variable capacitors; and othercomponents commonly used in the implementation of high frequency devicesand systems, are batch fabricated and packaged onto and within asuitably patterned and adjoined multiple layered stack of LTCCsubstrates. The discrete components can be separated from the substratesusing any of the well known and established methods of die separationsuch as diesawing.

[0034] In yet another embodiment of the present invention a phased-arrayantenna is a multi-layered structure, which contains a sub-array ofwide-band radiating patches, a corresponding number of digital phaseshifters, a power divider (or combiner) network, and a band pass filterat the input (or output) of the antenna. The antenna layers preferablyuse LTCC material as a dielectric substrate and the various circuitcomponents formed by the different layers are integrated together viavertical interconnects. This level of integration and the use of LTCCmaterial results in a rugged and power efficient antenna, which allows asignificant reduction in the cost of phased-array antenna systems, whileimproving the overall performance of such systems. The modularity of oneembodiment of the design greatly simplifies the integration of the largephased-array that can be assembled using the antenna modules of thepresent invention as its building blocks. Similar designs are employedfor the transmitting and receiving antennas.

[0035] Alternatively, the entire antenna system can also be implementedusing a multiplicity of suitably patterned and adjoined large sheets ofLTCC material unto which the various components are fabricated to embodya complete and functional phased-array antenna system. In yet anotherembodiment of the present invention, micromechanical and microelectroniccomponents, either discrete or integrated onto substrate materials whichhave high-performance characteristics at elevated operationalfrequencies, are fabricated, integrated and packaged on LTCC substrates.

[0036] According to the method of the present invention, the use oflarge LTCC wafers or panels, without compromising processing capabilityor speed, lowers the cost of fabrication dramatically. Panels as largeas 1×1 m can be manufactured in LTCC lines, as compared to 0.3 mdiameter wafers used in state-of-the-art semiconductor IC foundries.Moreover, the tools and fabrication methods needed to process large LTCCpanels are not as expensive as those needed to process semiconductorwafers, since the minimum size of patterned features, such as conductingstrips and via holes, is more than 25 μm. The savings on the tool costsand the fabrication of significantly more devices for the equivalenteffort and cost yields very low-cost fabrication.

[0037] Alternatively, LTCC substrates can be embodied in the form ofwafer sizes and dimensions standard to the semiconductor processingindustry and equipment set, thereby allowing the fabrication ofhigh-performance devices and systems on the existing semiconductorprocessing equipment base.

[0038] The method of the present invention also does not requireseparate packaging and integration steps for the MEMS components. In thepresent invention, a multiplicity of suitably patterned LTCC materiallayers are stacked or adjoined together and used as substrates ontowhich are fabricated high-performance MEMS components that are requiredto build high frequency devices and systems including: MEMS tunableinductors; electronically tunable variable inductors; closed-loopcontrolled electronically tunable variable inductors;electronically-controllable phase-shifters; RF switches; variablecapacitors; electronically tunable variable capacitors; closed-loopcontrolled electronically tunable variable capacitors; and othercomponents commonly used in the implementation of high frequency devicesand systems.

[0039] Alternatively, a variety of MEMS devices and other components,some of which are fabricated directly onto the LTCC systems, others ofwhich are made on other substrates such as microelectronics die, can beintegrated with the LTCC layers to build a phased-array antenna, orother high frequency devices and systems.

[0040] These components that can be fabricated on the LTCC substratesfor the embodiment of RF systems or phased-array antennas including, forexample, transmission lines, couplers, dividers, filters and radiatingpatches.

[0041] Providing the vertical connections between layers necessary foran array antenna, a discrete MEMS component, or an array of MEMScomponents, is straightforward and efficient in an LTCC process, whetheron a panel, sheet or wafer shaped substrate, in comparison to standardsemiconductor processes using conventional substrate materials, andwhere such connections are extremely difficult and expensive.

[0042] According to the method of the present invention, two or moremultilayer ceramic modules or substrates are formed using a standardLTCC process are combined with microfabrication processes as part of thepresent invention. After appropriate surface preparation on one of themodules or substrates, MEMS devices are formed on the frontside of thatmodule or substrate. Next, the two ceramic modules or substrates arebonded or adjoined together, forming a hermetically sealed cavity inwhich the MEMS devices are located. The bonding is preferably performedin a controlled environment to modify and improve the operation of theMEMS devices. Finally, various types of ICs can be flip-chip bonded orwire bonded to the backside of the module on which the MEMS devices arefabricated. These ICs can also be packaged by bonding or adjoining twoor more modules or substrates to form a sealed cavity. At this step, ifnecessary, thermal spreaders are then mounted on the ICs. It should beobvious to those skilled in the are that this method can be extended asa low-cost and efficient method to package a variety of other highfrequency micromechanical, electronic and microwave components andsystems. Efficient electrical connections between components and systemslocated on different layers of the stack of multiple layers are enabledwith this method.

[0043] From the point of view of MEMS fabrication, for an embodiment ofa phased array antenna, one or more ceramic modules are the substrateson which the MEMS devices are fabricated, and the other modules are thetop cover of a hermetically sealed cavity containing the MEMS devices.From the point of view of the phased-array antenna, the layer of MEMSdevices is only one of many device layers that make up the overallarchitecture of the antenna. The layer with the MEMS devices (andcorresponding transmission lines) is referred as the phase-shifterlayer. The other ceramic layers that form the ceramic modules are usedto form circuits, such as power dividers or combiners, filters,couplers, polarizers, etc. Finally, for semiconductor Ics, the ceramicmodules can also serve as the integration and packaging medium.

[0044] The phased array antenna and phase-shifter combination of thepresent invention results in a design in which there are many antennaradiating elements with slight phase-shifts with respect to each other,thereby allowing the use of an electronically scanable beam withoutmechanically changing the position of the phased array antenna.

[0045] The present invention also results in an extremely low-costmethod for batch fabricating and packaging discrete MEMS, electronic andmicrowave components. The present invention also results in an extremelylow-cost method for batch fabricating and packaging discrete MEMS RFswitches and integrated MEMS phase-shifters.

[0046] The present invention also results in an extremely low-costmethod for batch fabricating and packaging integrated MEMS tunableinductors; electronically tunable variable inductors; closed-loopcontrolled electronically tunable variable inductors; RF switches;electronically-controllable phase-shifters, variable capacitors;electronically tunable variable capacitors; and closed-loop controlledelectronically tunable variable capacitors, as well as combinations ofthe above devices.

[0047] The present invention also results in an extremely low-costmethod for batch fabricating and packaging integrated phased-arrayantennas, and, in particular, integrated phased-array antennas that canbe subsequently tiled together with a number of identical antennamodules to form an entire phased-array antenna system.

[0048] The present invention also results in an extremely low-costmethod for batch fabricating and packaging high quality MEMS devices andother electronic and microwave components on LTCC substrate materials.

[0049] The present invention is directed to the embodiment of MEMSdevices and systems, in particular RF MEMS devices and systems onto orwithin LTCC substrates. The present invention is also directed to theembodiment of discrete MEMS, electronic, and microwave components ontoLTCC substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 shows two perspective views of a preferred embodiment of ageneralized MEMS device or system of the present invention fabricated onand packaged within a stack of multiple layers of LTCC material, wherethe device or system has been sliced open to show its internalstructure.

[0051]FIG. 2 is a cross-sectional view of the preferred embodiment of ageneralized MEMS device or system fabricated on and packaged within astack of multiple layers of LTCC material, which shows electricalconnections through the stack of layers of the LTCC material and theintegration of an IC substrate with the MEMS on LTCC substrates to makea functional system.

[0052]FIG. 3 is a perspective view of the preferred embodiment of ageneralized MEMS device or system fabricated on and packaged within astack of multiple layers of LTCC material which encloses multiple MEMSdevices with the two LTCC modules being separated for ease inunderstanding the configuration.

[0053]FIG. 4 illustrates a process flow for making the generalized MEMSsystem of the present invention using LTCC materials.

[0054]FIG. 5 illustrates the process flow for standard LTCC fabrication.

[0055] FIGS. 6A-6D are graphs showing non-contact surface measurementsof a multilayer ceramic substrate with a through-wafer gold via aftermechanical polishing.

[0056] FIGS. 7A-7D illustrate the process for hermetically packaging theMEMS devices.

[0057] FIGS. 8A-8F show a traditional MEMS process flow that can also beused with the present MEMS device or system invention.

[0058]FIG. 9A is a perspective view of the preferred embodiment of aMEMS tunable variable capacitor device or system fabricated on andpackaged within a stack of multiple layers of LTCC material.

[0059]FIG. 9B is a cross-sectional view of the single tunable capacitorpackaged in an LTCC module.

[0060]FIG. 9C illustrates the operation of the tunable capacitor of FIG.9B according to the present invention.

[0061]FIG. 9D is a cross-sectional view of the preferred embodiment of aMEMS closed-loop controlled tunable variable capacitor device or systemfabricated on and packaged within a stack of multiple layers of LTCCmaterial combined with an Integrated Circuit (IC) die.

[0062]FIG. 10A is a schematic view of the tunable (switched) inductor.

[0063]FIG. 10B is a cross-sectional view of the tunable (switched)inductor.

[0064]FIG. 11A is a schematic view of a generic tunable inductor-tunablecapacitor network.

[0065]FIG. 11B is a cross-sectional view of the generic tunableinductor—tunable capacitor network.

[0066]FIG. 12A is a partial perspective view of the preferred embodimentof integrated phased-array antenna system of the present inventionshowing some of the plurality of sub-array modules used to form thephased-array antenna.

[0067]FIG. 12B is a perspective view of the preferred embodiment of thesub-array module which includes a 4×4 array of radiating elements.

[0068]FIG. 12C is a perspective view of a single radiating element ofthe sub-array module.

[0069]FIG. 13 is a cross-sectional view of a single radiating element ofthe sub-array module.

[0070]FIG. 14A illustrates a cross-sectional view of the LTCC modulethat supports the MEMS phase shifters.

[0071]FIG. 14B illustrates a cross-sectional view of the LTCC modulethat covers the MEMS phase shifters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072]FIG. 1 shows two perspective views of a sliced open generalizedMEMS RF device or system (“module”) 10 fabricated on a stack of multiplelayers of an LTCC material which serve as a substrate 11 for afabricated MEMS RF device 14. FIG. 1 also illustrates the packaging ofthe MEMS RF device wherein a cavity 13 is formed in a stack of LTCClayers 22 which are mated together to form a second substrate 12. Thetwo substrates are then bonded or affixed together so as to enclose theMEMS RF device 14 within the cavity formed 13 in the upper LTCCsubstrate 12 prior to bonding the two LTCC substrates together to formdevice 10.

[0073]FIG. 2 illustrates a cross-sectional view of the preferredembodiment of a single generalized MEMS RF device 10 fabricated on astack of multiple layers of LTCC material 22 and demonstrates theability of providing suitable electrical connections 16 and 39 through amultiplicity of layers of the LTCC substrate 11 as well as the abilityto form electrical connection paths 17 and 23 and passive or activecomponents 24 and 25 on the substrates, thereby achieving an efficientand cost effective means to integrate and package MEMS RF devices.

[0074]FIG. 3 shows a perspective view of a multiplicity of generalizedMEMS RF devices 33 formed simultaneously on an LTCC substrate 31 (i.e.,batch fabricated). It should be obvious to those skilled in the art thata multiplicity of MEMS RF devices or systems can be fabricated,integrated and packaged simultaneously, using so-called batchfabrication methods whereby the processing costs for a substrate aredistributed over the number of working components on the same substrateor module.

[0075] Referring to FIG. 2, the MEMS RF devices 14 comprising the MEMSsystem 10 of the present invention are enclosed within two multilayerLTCC modules 11 and 12, the layers of which form various systemcomponents, including at least one MEMS RF device 14, a packaging cavity13, and horizontal and vertical interconnects 16 and 39. The preferreddielectric medium for implementing these components is a low-temperatureco-fired ceramic, or LTCC, which allows multilayer processing, and thusfacilitates the vertical integration and multilevel electricalconnection of the component layers and devices at the processing stage.

[0076] Although LTCC is the preferred dielectric medium for the presentinvention, it is also possible to use high temperature co-fired ceramic(“HTCC”) for the dielectric medium. The number of MEMS RF devices andelectrical elements in each device or module 33 (in FIG. 3) depends onthe frequency, performance, maximum package size, and system, processingsteps and power distribution requirements of the system. The level ofintegration depends on the size and complexity of the MEMS RF systemrequirements.

[0077] Device 10 (FIG. 2) includes at least one MEMS-based RF element 14that is fabricated on LTCC module 11. Minimization of the die area isvery important to lower the cost of the overall system, since thepackaged MEMS RF devices are typically the most expensive component ofsuch a system.

[0078] The vertical integration benefits of LTCC technology and thehigh-performance of MEMS RF devices are crucial for achieving thelow-cost high-performance RF devices 10 of the present invention.Despite recent developments in LTCC processing (for example,photolithographic patterning of conductor/dielectric layers, zero-shrinkprocesses that lower the shrinkage in the X-Y plane more than one orderof magnitude, and various new dielectric and magnetic layers) thepreferred design flow of the present invention employs only techniquescurrently available in the mainstream of LTCC processing. However, useof the recent developments in LTCC processing can increase dimensionalcontrol and device density, and decrease the volume and reduce the costof fabrication even further.

[0079] The process used to make each MEMS RF device 14 of system 10 isgenerally shown in FIG. 4. According to the process of the presentinvention, the two multilayer ceramic substrates 11 and 12 are formedusing a standard LTCC process 40. The standard LTCC process flow isillustrated in FIG. 5. After the surface preparation on the substrate11, MEMS components are formed on the frontside of the module as shownat step 41 in FIG. 4. Next, at step 42, the LTCC substrates 11 and 12are bonded, forming hermetically sealed cavities 13, in which the MEMScomponents 14 are located. The bonding of substrates 11 and 12 can beperformed in a controlled environment to achieve the hermetically sealedcavity 13: Operation in this sealed cavity improves the operation ofMEMS devices 14.

[0080] From the point of view of MEMS fabrication, LTCC substrate 11 isthe substrate on which MEMS RF devices 14 are fabricated, and the otherLTCC substrate 12 is the top cover of the hermetically sealed cavity 13formed by the bonding of substrates 11 and 12. From the point of view ofthe module or package, the layer 26 that contains the MEMS RF components14 is nothing more than one of many device layers that make up theoverall architecture of system 10. This layer, which includes MEMS RFcomponents and potentially other components, is referred as the MEMSlayer 26. Other circuit components layers 27, 28, and 38 are formed inthe LTCC substrates 11 and 12.

[0081] The two multilayer LTCC substrates 11 and 12 forming module 10are formed and fired separately using the standard LTCC fabricationprocess shown in FIG. 5. LTCC technology is inherently cost-effectivecompared to any fabrication technology with traditionalphotolithographic processing. The patterning of layers at step 110 isperformed in a single step, as opposed to 8-10 steps in traditionalphotolithography. Secondly, via holes can be opened at step 112 andfilled at step 114 with conductor inks effortlessly. This allowsconstruction of multiple layers at step 116, forming an integratedsystem 10 in one package, as shown in FIG. 1. The process of FIG. 5eliminates all of the packaging issues regarding the MEMS RF devices andassociated passive layers, such as resistors, capacitors, electricalvias, and electrical interconnects. Although current LTCC fabricationlines handle 15×15 cm plates, the fabrication capability for 45×45 cmplates has been demonstrated and can be further extended up to 100×100cm. Therefore, it is possible to obtain large numbers of MEMS RF devicesfrom a single LTCC plate. The LTCC technology allows the integration andpackaging of all the device layers necessary for the system 10, exceptone layer, i.e., the MEMS layer 26.

[0082] The MEMS RF devices 14 are fabricated directly on layer 29 ofLTCC substrate 11. Minimum features (as small as 1 μm) required for MEMSRF devices or systems 14 are considerably smaller than what can beachieved (>100 μm) by using screen-printing techniques. Therefore, thesurface of buffer layer 29 must be prepared for photolithography steps.The minimum feature achievable using lithographic patterning on LTCCwith an unprepared surface is about 20 μm. To overcome this limitation,the present invention uses special surface preparation techniques, suchas chemical-mechanical polishing, combined with thin-film depositiontechnology, photolithography and etching technologies to obtain therequired resolution for MEMS RF devices and systems 14 on LTCC layer 29.These MEMS RF devices 14 are then packaged when LTCC substrates 11 and12 are bonded together, and cavity 13 in module 12 is placed on top ofthe MEMS RF devices or systems 14.

[0083] Both LTCC substrates 11 and 12 include numerous verticalconnections 16, and 39 and screen-printed conducting layers 17 and 23between the dielectric layers 22 comprising each system 10. The verticalconnections 16 and 39 are preferably metal-filled via connections. Tominimize coupling between different device layers in high frequencyapplications, stripline topology is preferred for the electrical devices28 fabricated in the internal layers of LTCC substrate 11.

[0084] For some applications, particularly high frequency applications,it is well known that different devices have different characteristicimpedance requirements. Termination resistors and other impedancematching components can be fabricated either in the internal layers ofsubstrate 11, such as “buried in” resistors 24 shown in FIG. 2, in whichcase they will vary ±20% around a mean value. The termination resistorscan also be located on a surface 25 of the LTCC substrate 11 where theycan be trimmed to higher accuracy such as ±1%.

[0085] The screen-printed or photo patterned layers 17, and 23 areburied metal patterns which are used to define interconnections andpassive electronic or microwave devices, such as resistors, capacitors,inductors, transmission lines, couplers, dividers, etc. The resistanceof resistors on the surface 25 of LTCC substrate 11 or through thelayers of LTCC material forming substrate 11 can be controlled by thedimensions of these metal lines. Similarily, the values of other passivecomponents can be adjusted by suitably varying the dimensions of thesecomponents. For example, the characteristic impedance of thetransmission lines is preferably controlled to be in the range of 30ohms to 100 ohms. This can be done by controlling the thickness of theceramic dielectric layers 22 and the width of the signal conductorfollowing well known formulas available in the literature for a varietyof transmission line configurations.

[0086] Preferably, the material system used for dielectric layers 22 is943 Green Tape™, a product made by Dupont. The use of 951 Green Tape™,another product made by Dupont, for dielectric layers 22 allows theunacceptable losses of LTCC materials at higher frequencies (20 GHz andabove) to be avoided. DuPont's 943 Green Tape is a gold, silver andmixed metal compatible low-loss, low CTE, lead free glass/ceramic tape,which allows transmission line losses as low as 0.2 dB/cm at 30 GHz tobe achieved. However, presently, Dupont 943 has only one thickness ofdielectric tape. The dielectric constant (ε_(r)) and the loss tangentsof Dupont 943 dielectric sheets are 7.5±0.1 and 0.001, respectively.(Reference 99% alumina, a well-known microwave substrate, has adielectric constant of 9.6 and a loss tangent of 0.001). Using theDupont 943 material system to form LTCC modules 11 and 12 allows lowcharacteristic impedance values (<40 ohms) to be obtained, if the signalplane 23 is separated from top and bottom ground planes 17 (forsymmetric stripline configuration) with a single dielectric material asis important for high frequency applications. Device layer 28 shown inFIG. 2 illustrates cross-sectional views of symmetric striplineconfigurations. The stripline in layer 28 consists of three conductiveplanes: two of them ground planes 17 and a signal plane 23 in themiddle. Vertical connections 39 connects signal plane 23 from one deviceto another one by going through the ground planes 17. Based-on thelimitations on minimum patternable conductor width, high impedancevalues (>60 ohms) may require more than one LTCC layer on both sides ofsignal plane 23. If the minimum line width is around 100 μm (as in thecase of most screen-printing based patterning techniques), then toachieve 50 ohm lines in a Dupont 943 LTCC system (ε_(r)=7.5 and firedthickness ˜110 μm) two dielectric layers 22 have to be used on bothsides of signal plane 23.

[0087] As shown in FIG. 2, in the preferred embodiment of the invention,the RF device layer 28 in LTCC substrate is formed using two layers of943 dielectric tape 22. Of course, the number of layers needed wouldchange if a different dielectric with different properties andthicknesses were used.

[0088] A stripline transmission line configuration is preferable becauseground planes 17 on both sides of the stripline circuits help minimizethe interference between circuits in the different layers 28, 26 and 38.Therefore, the electromagnetic isolation between the vertical circuitsis easier to achieve. In addition, the stripline configuration has ahomogeneous dielectric medium, which lowers signal dispersion.

[0089] Other transmission line configurations, such as shielded-coplanartransmission lines, can be used in the internal device layers such as28. At outer surfaces, variations of microstrip and coplanarconfigurations can be used. For the MEMS RF device layer 26, aconductor-backed coplanar configuration is preferable.

[0090] All the vertical connections 16 and 39 shown in FIG. 2 are thesame. However, functionally, there are important differences. Verticalconnections between the ground planes are not that critical for signalintegrity. On the other hand, connections between the signal planes areunderstandably more important. Vertical connections 16 are groundconnections for device layer 28, whereas vertical connections 39 aresignal connections for device layer 28 in FIG. 2. The shielding forvertical connections is important if they originate from a signal plane.Thus, the vertical connections between two layers of devices 39 can beunshielded or shielded coaxial-type connections. In both cases, verticalconnections 39 have to be designed carefully to minimize the internalreflections and losses between two layers of devices 28, 26, and/or 38.

[0091] Vertical connections 16 can be also used to shieldelectromagnetic interference and coupling. If there are multiplecomponents in a single layer, grounded-vertical connections 16 placedbetween them will lower interference significantly.

[0092]FIG. 2 also shows an Integrated Circuit (IC) substrate 19 beingmated to LTCC substrate 12 so as to provide active microelectronicfunctionality. FIG. 2 also shows an Integrated Circuit (IC) substrate 20mated to the LTCC substrate 11 so as to provide active microwavefunctionality.

[0093] To make proper electrical connection, ICs 19, and 20 can beflip-chip bonded to LTCC substrates 11 and 12 respectively. Copperthermal spreaders 21 can then be mounted directly on the backside of ICs20, if necessary. If IC power consumption is not an issue, then low-costwire-bonding techniques can also be employed to mount low pin-count ICs19 on LTCC substrate 12 (note that wire-bonding option is not shown inthe figure). Integrated circuits 19, and 20 can be any of the following:a control circuit for the MEMS RF components, a power module for suchMEMS RF components, a microprocessor or a signal processor, a poweramplifier, a low noise amplifier, or any other analog/digital integratedcircuits that are necessary for the operation of the RF system.

[0094] As illustrated in FIG. 2, lower LTCC substrate 11 has threedistinct functional areas, i.e., an interconnection layer 38, one ormore device layers 28, and a buffer layer 29. The interconnection layer38 is used to interconnect through connections 18 and 39 different ICs20 and lumped components such as inductors, capacitors, and resistors25, either discrete or formed in or on the LTCC substrate 11. The devicelayer 28 is distributed or lumped, as necessary, for proper operationdepending on the frequency. If there is more than one device layers,they are connected together by a connection 39 extending between suchlayers. Several device layers can be integrated vertically in thissection as needed for the application.

[0095] The buffer layer 29 is used only for connection, through avertical connection 16 and 39, to the MEMS RF devices 14, which areformed on top of this layer. Since the front surface 71 (in FIG. 6) oflayer 29 is polished prior to the fabrication of the MEMS RF devices 14on top of layer 29, no surface conductors are printed prior topolishing. In the preferred process flow, LTCC compatible bondingmaterials are printed and fired after polishing. However, it is possibleto have one un-patterned conductor layer, which is deposited as a partof the LTCC process. In this case, the surface preparation would includemetal polishing rather than ceramic polishing, and the MEMS processsequence shown in FIG. 4 must be modified accordingly.

[0096] The second LTCC substrate 12, as shown in FIG. 2, also can have amultiplicity of functional layers, including a MEMS cover layer 37 andone or more device layers 27, depending on the exact designconfiguration. MEMS cover layer 27 includes a cavity 13 for MEMS devicesand systems 14 that enables proper packaging of the MEMS devices andsystems 10 fabricated on LTCC substrate 11. Device layer 27 is one ormore layers of passive devices. One or more connections can be made tothe shielding ground plane 17.

[0097] Surface preparation for buffer layer 29, which acts as asubstrate for the fabrication of MEMS devices 14, can potentiallyinclude multiple steps such as planarization of ceramic parts,planarization of first metallization, and deposition of bondingmaterials. The last two items are optional because it is obvious tothose skilled in the art of hermetic packaging and MEMS fabrication thatthere are many different ways to achieve the desired hermetically sealedcavity formed by the bonding of the two LTCC substrates 11 and 12.

[0098] Surface planarization is necessary prior to MEMS fabrication dueto large surface roughness of fired ceramic parts. The surface roughnessis determined both by the intrinsic roughness of dielectric sheets andburied features underneath the surface. Typically the contribution fromthe latter source is more important; however, even the intrinsicroughness (R_(a)) for fired Dupont 943 dielectric sheets is on the orderof 1 μm. Accurate, high-yield, and reliable fabrication of MEMS RFdevices necessitates R_(a)<0.1 μm. R_(a) is the average surfaceroughness calculated as an average of several point measurements takenwith a single scan. If the MEMS process starts with such smoothsurfaces, MEMS RF devices with features as small as 1 μm or less can befabricated. To accomplish this goal, the fired LTCC plates (or wafers)on which the MEMS processing is performed are lapped and polished.

[0099] Regular ceramic polishing has common problems, such as dishingand erosion. Dishing and erosion are forms of local planarization wherecertain areas of the wafer polish faster than others. In dishing, asofter material (e.g., metals) is “dished” out of the lines, where as inerosion whole sections of the ceramic are polished faster than othersare. As shown in FIGS. 6a through 6d, these are not particularlyimportant problems for the MEMS RF devices, as long as such devices areplaced outside the dishing and erosion area 72, which, as shown in FIGS.6a through 6 d, is less 250 μm from the center of vertical connection71. In certain design configurations of the present invention, it may bedesirable to reduce or eliminate dishing. For example, this may beimportant for optimization of the use of the surface area of the ceramicsubstrate, i.e., more devices and components per square area ofsubstrate. Dishing can be reduced or eliminated by optimization of theplanarization slurry, adjustment of the polishing force, varying thepolishing pad spin rate, use of an optimize polishing pad, etc., as wellas the addition of another planarization for the first metallizationused in the MEMS process. Alternatively, dishing can be reduced oreliminated by application of a suitably patterned protective layer onthe surface of the exposed metalized areas prior to the planarizationprocess. This allows the ceramic material to be exposed to theplanarization process while the metal is protected. This protectivelayer is subsequently removed after the planarization is complete.

[0100] Another optional step, which can be done as a part of surfacepreparation, is the deposition of bonding materials on the surface ofbuffer layer 29 prior to MEMS processing. LTCC material systems usuallyinclude a low-temperature, two-component bonding/brazing materials suchas Dupont 5062/5063. This particular brazing system is used in severalapplications that require hermetic sealing in demanding spaceapplications. Other alternatives include using regular flip-chip bondingtechniques and dielectric bonding, such as glass-frit bonding. If theMEMS RF devices can sustain elevated processing temperatures, thesematerials can be deposited after the MEMS process. If not, as in thecase if Dupont 5062/5063, they must be prepared before the MEMS partsare fabricated. In the preferred embodiment of the invention, a Dupont5062 adhesion layer and a Dupont 5063 soldering conductor are depositedand fired at >800° C. following manufacturers suggestions. This processis illustrated in FIGS. 7a through 7 d, and needs to be done on bothbonding surfaces of the LTCC substrates 11 and 12. Bonding can be doneusing eutectic bonding, or bonding using insulating layers, such asglass-frit or thermalsetting polyimide films, etc.

[0101] According to the process shown in FIGS. 7a through 7 d, the frontside 73 of ceramic substrate 11 is planarized, whereby contacts 74 areexposed, which are vertical connections, such as 39 in buffer layer 29,protruding through. Thereafter, as shown in FIG. 7b, the Dupont5062/5063 brazing system is screen-printed on external bond pads 74. Inthis step, a Dupont 5062 adhesion layer 75 and a Dupont 5063 solderingconductor 76 are deposited on the contact pad 74 and fired at >800° C. Aseal ring 15 is also formed around MEMS RF device and system area 77.

[0102] A MEMS fabrication process (see FIGS. 8A-8F) is then carried outon the front side 73 of ceramic substrate 11 so that MEMS devices andsystems 14 are formed in the MEMS device area 77. Similarly, on the backside 80 of ceramic substrate 12, shown in FIG. 7d, is alsoscreened-printed with the Dupont 5062/5063 two-component brazing systemin a manner similar to that used with ceramic substrate 11. In the caseof ceramic substrate 12, a Dupont 5062 adhesion layer 82 and a Dupont5063 soldering conductor 84 are deposited on contact pads 78, and a sealring 88 is deposited around a cavity 13 which is designed to accommodatethe MEMS RF devices 14 when the front side 73 of ceramic substrate 11and the back side 80 of ceramic substrate 12 are bonded together. Thebonding of these two modules is preferably done at a low-pressure in alow-humidity environment.

[0103] Once the surface preparation is completed, the MEMS fabricationprocess can start. Various MEMS process flows, which do not require hightemperature, can be followed. One possible MEMS process flow for a RFswitch is shown in FIGS. 8A-8F.

[0104] The process flow illustrated in FIGS. 8A-8F involves three metaldepositions. The first metal is used to define the planar waveguidestructures. In FIG. 8A, a preferred configuration 120 for coplanarwaveguides with finite-ground-plane extension is shown. Configuration120 is the three metal depositions 122 shown in such figure. The twooutmost strips 124 are used for electrical connection to an air-bridge.This first metal 120 can be deposited on LTCC wafer 118 typically usinga physical deposition method, such as evaporation, sputtering orelectrochemical deposition, and then it is patterned one of two possibleways. If the desired film thickness is relatively thin compared to thethickness of the resist or masking layer, it can be patterned using awell-known fabrication technique called “lift-off”.

[0105] Typically, to lower the propagation losses at high frequencies(>1 GHz), metals with low resistivity values, e.g., gold, silver andcopper, are preferred. In addition, thick metals (t>1 μm) are morefavorable to lower the resistive (ohmic) losses. As thickness of metalfilm 120, increases relative to the thickness of the resist or maskinglayer, it gets more difficult to use lift-off patterning. Instead,patterning using a “mask and etch” process becomes more favorable. Inthe sequence, first metal 120 is etched using a photoresist mask, whichis patterned using a standard photolithography step. As is known bythose skilled in the art of integrated circuit fabrication, it ispossible to have even thicker metal patterns using photoresist moldingand electro or electroless deposition methods. Generally, such methodsmay also require additional planarization step to eliminate localthickness variations. In addition, it may be desirable to add anadhesion layer to improve the adhesion between the desired metal filmand the substrate. The resulting pattern is shown in FIG. 8A.

[0106] Next, a sacrificial layer 126 is deposited to form the air gapnecessary for the operation of the switch. Many types of sacrificiallayers can be employed at this step. The key is selectivity of releaseetch. The sacrificial layer 126 must be chosen such that the metal doesnot get etched during the release etch. As described in U.S. Pat. No.5,578,976, certain polyamides layers can be used as a sacrificial layersince these films can be easily removed in O2 plasma without significanteffect on exposed gold metal conductors. Another important factor forselection of a suitable sacrificial layer is the deposition temperatureof the sacrificial material 128. It must be low enough so that it can bedeposited after the first metal layer 120 is already on the substrate.In the preferred method, PlasmaEnhanced Chemical Vapor Deposited (PECVD)silicon dioxide can be used as a sacrificial layer material since thismaterial can be deposited at sufficiently low temperatures that themetal layers are not affected. These PECVD silicon dioxide films can besubsequently removed in an buffered oxide etch or diluted hydrofluoricacid solution without degradation of the gold metallization as shown inFIGS. 8A to 8F. If the thickness of waveguide layer 120 is more than 3μm, it is preferable to use a planarization such as chemical-mechanicalpolishing step after silicon dioxide deposition.

[0107] The thickness of sacrificial layer 126 may vary depending on theswitch requirements. Typically, it is between 2-4 μm thick. The mostimportant consideration is the OFF-state capacitance of the switch. Thevalue of the OFF-state capacitance decreases as the height of the bridge(the thickness of the sacrificial layer) increases. FIG. 8B shows thesacrificial layer after anchor patterning.

[0108] The rest of the process steps shown in FIGS. 8C to 8F relate toformation of an air-bridge, which is well know in the art. First, thecontact metal 128 is formed using lift-off or direct patterning on topof sacrificial layer 126 using physical deposition as illustrated inFIG. 8C. Next, a structural layer 130, for example plasma enhancedchemical vapor deposited silicon nitride layer, is put down andpatterned (FIG. 8D). Then, the third metal 132 is formed again usinglift-off or direct patterning as shown in FIG. 8E. Finally, thesacrificial layer 126 is selectively etched releasing the air-bridge134, as shown in FIG. 8F, in this case using buffered oxide etch ordiluted hydrofluoric acid solution. To improve the etch performance itis customary to add etch holes if the areas to be released are widerthan 100 μm. Finally, to minimize the effect of stiction, asupercritical point CO2 dryer may be used.

[0109] Air-bridge 134 can be formed by other fabrication methods aswell. Although low-loss requirements may favor thick plated bridges,mechanically such bridges are not very robust; therefore, thinner buthigher quality films may be preferable instead. But if quality is moreimportant, it is possible to increase the thickness of the second metallayer 130 using electro or electroless deposition techniques.

[0110] The fabricated air-bridge 134 can be used as an electrostaticallyactivated MEMS RF switch simply by applying a voltage between groundplanes and the air-bridge 134. With the applied voltage, bridge 134 ispulled down, resulting in very high capacitance between the ground planeand signal line, thus essentially shorting the signal line to ground atfrequencies above 1 GHz. When the potential between the plates isremoved, air-bridge 134 will restore itself to its original form due tothe mechanical restoring force of the upper electrode of the switchdevice. Several MEMS sequences described in the following patents andpublications could be used instead. U.S. Pat. No. 6,069,540, issued June1999; D. Hyman, et al. Electronics Lett., vol. 35, no. 3, pp. 224-226,Feb. 1999; S. Pacheco, et al. Proc. IEEE MTT-S Int. Microwave Symp.,pp.1569-1572, June 1998; S. -C. Shen, et al. Dig. IEEE IEDM Int.Electron Devices Meet., Dec. 1999. Additionally, other actuation methodsmay be used including piezoelectric, thermal bimetallic, shape-memoryallow, etc.

[0111] To prevent stiction between contact surfaces of MEMS RF switch,and to maintain low-resistance contacts in switches, surface treatmentsmay be necessary to avoid contamination and unwanted chemical reactions,such as oxidation. Commercially available anti-stiction coatings, suchas the dichlorodimethylsilane (DDMS) monolayer, theoctadecyltrichlorosilane (OTS) self-assembled monolayer, or similarproducts can be used on the metal surfaces to minimize any unintentionaladhesion in mechanical switches or other contacting or near-contactingsurfaces within the present invention.

[0112] The MEMS processing can be performed on large-area-processing(LAP) equipment (not shown). This equipment, like LTCC processing tools,can handle very large panels (or wafers). The current generation of theLAP tools has the capability of processing panels larger than 800×800 mmand capable of handling minimum features as small as 2 μm or less. Onthe other hand, current generation of LTCC manufacturing tools canprocess only 200×200 mm panels, though it is straightforward for sizesto 800×800 mm and beyond.

[0113] The MEMS fabrication is followed by the bonding of the two LTCCsubstrate 11 and 12 at low pressure and in a low-humidity environment.If other bonding techniques were used, the necessary surface preparationwould precede the selected bonding process. The bonding of ceramicsubstrates 11 and 12 can then be followed by the integration of ICs 19and 20 and other discrete components (not shown) on the backside ofceramic substrate 11 (see FIG. 2). For this purpose, flip-chip bondingis more reliable and repeatable, and lends itself to better thermalmanagement options, as described below. Therefore, especiallyhigh-power, high-frequency ICs 20 are preferably flip-chip bonded inshielded cavities in ceramic substrate 11 to minimize theelectromagnetic coupling to other sensitive circuits and to achievebetter heat removal from the backside of ICs 21. ICs 19 and 20 can beanalog or digital ICs, MMICs and/or Radio Frequency Integrated Circuits(“RFICs”). There is no clear distinction between these two terms, thoughtypically RFIC is used for chips with operating frequencies <10 GHz.

[0114] The quality of flip-chip bonds are assessed by determining thedetuning of the circuits due to their proximity to ceramic substrate 11,the reflection due to transition, and the insertion loss at eachconnection. Typically, the size of the pads 18 (in FIG. 2) and the metalextensions are preferably selected to be as small as possible tominimize parasitic capacitances. The height of the pads 18 is typicallychosen to be larger than one third of ground-to-ground spacing on the50ΩQ CPW lines on chip to minimize the detuning. By careful placement ofcontact pads 18, and if necessary, inductive compensation, a return lossabove 25 dB at 40 GHz and an insertion loss of less than 0.25 dB can beachieved.

[0115] Dupont 943 dielectric tape has thermal conductivity of ˜5 W/mK.This conductivity can be further improved by using conductor-filledthermal vias 16 and 39. It has been shown that with proper thermaldesign, it is possible to obtain thermal conductivities close to thoseof costly Beryllium Oxide (“BeO”) and Aluminum Nitride (“AIN”) (>250W/mK) substrates. Here, thermal spreaders 21 are mounted on the backsideof the flip-chip bonded ICs 20. If the device is placed in a shieldedcavity which is the same as the thickness of ICs 20, the thermalspreader 21 will function as an electromagnetic shield too.

[0116] The fabricated air-bridge 134 (in FIG. 8F) can also be used as anelectrostatically activated MEMS variable capacitor simply by applying avoltage between ground planes and the air-bridge 134. With the appliedvoltage, the bridge 134 deflects under the electrostatic force andthereby changes the separation between the two capacitor electrodesresulting in a changing capacitance of the device. The MEMS-basedvariable capacitor can be operated without reaching the pull-in voltageor can be operated beyond the pull-in voltage, depending on the exactdesign configuration.

[0117] The MEMS-based electronically-tunable variable capacitor is shownin three-dimensional perspective in FIG. 9A in cross section in FIG. 9B.As shown, the device merges an electrostatically actuatedmicromechanical variable capacitor device 50 on a multi-layeredsubstrate material 11 having continuous electrical connections 39through the layers of substrate 11. The same substrate material 22 isused to enclose the device by selectively removing a portion of theupper substrate 12 so as to form a cavity 13. The two substrates 11 and12 are then bonded together to enclose and protect the variablecapacitor 50.

[0118] The package containing the variable capacitor device 50 is ableto be surface mounted onto a ceramic or PCB as shown in FIG. 9B .Electrical connections 39 to device 50 are made to the externalconnections 18 on substrate 11 using solder and similar techniques.

[0119] Electrostatic actuation is the preferred method of embodying anelectronically controllable moving electrode for a variable capacitordevice 50. Electrostatic actuation is an extremely popular technologyfor the implementation of movable devices that require small to moderatedisplacements in combination with high operating frequencies.Additionally, electrostatic actuation is the preferred method ofactuation for MEMS devices made using surface micromachining techniques,such as in the present device 50.

[0120] There are two undesirable issues related to the use ofelectrostatic actuation that must be addressed during the design of awide dynamic range variable capacitor device. The first issue withelectrostatic actuators is the potential instability (sometimes termed“collapse voltage” or “pull-in voltage”) of the compliant electrode 51toward the fixed electrode 52 as the gap between the electrodes isdecreased with increased actuation voltage. This occurs since theelectrostatic force is inversely proportional to the square of theelectrode separation, whereas the counteracting mechanical restoringforce is typically only linear with displacement (assuming a perfectspring for the mechanical restoring force). It can be shown thatcollapse occurs in such a system when the displacement becomesapproximately ⅓ of the initial un-deflected electrode separation.Therefore, if collapse is to be avoided in the device, the initial gapin the structure must be designed to be at least 3 times the maximumrequired displacement of the upper electrode. Associated with thiseffect, is the fact that the applied actuation voltages will need to befairly high in order to move the upper electrode. This is because theinitial gap spacing between the drive and upper electrode 51 will needto be large, namely three times the useful movable range of upperelectrode 51 and the electrostatically generated force is proportionalto the inverse of the gap separation squared.

[0121] As a result of this effect, most of the electrostatic actuatedvariable capacitors reported in the past have had a limited tuningrange. Typically, the ranges of tuning that have been reported are nomore than 25%. Theoretically, the maximum tuning range is slightlyhigher, but far short of the tuning range needed for many applications.

[0122] An approach to overcome the tuning range limitation ofelectrostatically-actuated parallel plate configurations and animportant part of the present invention is to utilize a zipper actuationmethod as shown in FIG. 9C. In this approach the upper electrode 51intentionally comes into contact with the bottom electrode 52. As theactuation voltage is increased, an increased amount of area of the upperelectrode 51 is brought into contact with the bottom electrode 52 (FIG.9C). The applied DC voltage controls the shape of the upper electrode.The capacitance between the upper 51 and lower electrodes 52 changeswith the applied DC voltage. Furthermore, the shape of thecapacitance-voltage characteristic for the device is primarilydetermined by the geometry of the capacitor electrodes 51 and 52. Inthis approach, a dielectric layer 57, is required to prevent theelectrically conducting 56 part of upper electrode 51 from contactingthe conducting bottom electrode 52 (i.e., to prevent a short circuitbetween the electrodes). While not mentioned here, there are also othermethods to provide for an increased moving distance of the electrode andthereby increased tuning range.

[0123] The second issue is that the electrostatic force is notproportional to the applied actuation voltage, but varies with voltagesquared. In certain devices, such as clamped membranes or beams, it ispossible to modify the counter electrode to somewhat linearize therelationship between actuation voltage and displacement in a certainoperating range. For example, removing the counter electrode in thecenter area, it is possible to match the leveraging of the beam to thenon-linear relationship between actuation voltage and electrostaticforce, to achieve a close to linear relationship. For a suspendedstructure, the whole structure deflects uniformly and therefore theelectrostatic force will also be uniform, and there is no non-uniformityto match to the non-linear actuation force. One way to linearize theresponse would be to create non-linear suspension springs for thestructure, but this makes the design of the device difficult.

[0124] Even though the actuation force is a non-linear function of theapplied voltage for the non-contacting electrode arrangement, thisproblem can be reduced or nearly eliminated with the zipper electrodeconfiguration, as shown in FIG. 9C. In this configuration, thecapacitance can be made to vary nearly linearly with the applied voltageusing a specially designed electrode 51. The way this is done is to havethe area of the nearly contacting surfaces, namely after collapse of theelectrode into the mechanical stops 150, compensate for the non-linearelectrostatic versus voltage effect. Since the fabrications ofmechanical stops 150 adds several additional steps to the overall MEMSprocess sequence in FIG. 8A-8F, generally, the mechanical stops are notused in variable capacitors unless they are required to achieve acertain performance specification, such as voltage-capacitancelinearity.

[0125] Although electrostatic actuation for non-collapsing structurestypically require high voltages due to the inherently smallelectrostatic forces generated, this problem is lessened using zipperactuation. In this method, the initial electrode gap can be made quitesmall while still achieving a relatively large tuning range. Tuningratios in excess of 10 to 1 with applied voltages not in excess of 50Volts for the zipper actuator configuration are possible.

[0126] Although an electrostatic actuation mechanism using the zipperactuator approach is described, there are alternative methods ofelectrostatic actuation that can be used in the present invention. Forexample, another embodiment of the electrostatic actuated variablecapacitor would be to use a non-contacting actuator. This embodimentrequires the distance between the electrodes to be sufficient enough toavoid collapse, as described above. Another approach is to use anonlinear spring whereby the non-linearity of the electrostatic force iscompensated by the non-linearity of the mechanical restoring forcemechanism. Other approaches are also possible. The MEMS variablecapacitor can also be actuated using other means, such as bimetalliceffect, shape memory alloy, piezoelectrics, etc.

[0127] A substantial advantage of a electrostatically actuated variablecapacitor device of the present invention is that it can be made with arelatively simple and low-cost surface micromachining process asdescribed herein.

[0128] Another design issue of an electrostatically-actuated variablecapacitor is whether the device will be a one- or two-port device. Theadvantage of the one port, two terminal approach is that it is verysimple; however, the disadvantage is that the actuation voltage and thevoltage on the capacitor are coupled. A different approach and a featureof the preferred embodiment of the present invention is a two port, fourterminal design wherein separate electrodes are used to realize thevariable capacitor and the electrostatic actuator 51.

[0129] The LTCC material used for the substrate and package of thevariable capacitor has very low resistive losses at high frequencies,which is important in satisfying the requirements for this device. Thesubstrate material technology of the present invention is inherentlyvery cost-effective compared to alternative approaches, such asfabricating MEMS on silicon or MEMS on GaAs, while also allowing highfidelity photolithography to be used to make high-precision and highperformance micromachined elements. The substrate material is composedof a stack of layers 22 wherein each layer is uniquely patterned withopenings that are filled with low shrinkage conductive inks to provideelectrical connections through the layers 39. Metal lines or otherfeatures are patterned using photolithography on the surfaces of thelayers with a minimum resolution of approximately 20 microns. Thisresolution increases to 100 microns if the lower cost alternative methodof screen printing is used. The metal materials, which are deposited andpatterned on the substrate layers, are excellent conductors and includegold, silver and copper. These are the preferred conductor materials touse for microwave applications. The individual layers are stackedtogether and bonded to form a composite substrate in which electricalfeed-throughs span through multiple layers 22. Also, the metal conductorlines on the surfaces of the substrates 17 are enclosed with the stackedlayers 22. Passive components such as resistors and capacitors 25 (FIG.2) or ground planes 17 can be realized on the substrate surfaces 11 andsealed in the multi-layered substrate stack 24 (FIG. 2) depending on theexact design configuration. Additionally, cavities 13 can be carved outof the multi-layered substrates 11 that can be used to package amicromechanical element, such as a variable capacitor 50 or anintegrated circuit 19 or 20, as shown in FIG. 2.

[0130] An advantage of the preferred embodiment of the present inventionof the variable capacitor is that it enables the signal paths to beproperly shielded, as shown in FIG. 9B. Shielding is achieved on thesurfaces by appropriately laying out coaxial lines wherein the capacitorcontacts 56 and 52 have ground lines 17 on either side. The verticalconnections of the signal lines 39 can also be enclosed in a verticalground shields (not shown) to minimize interference between verticalsignal paths 39. This greatly improves the performance of the device atthe higher operational frequencies. While these kind of connections (notshown) are very useful for microwave components, they are in practicevery difficult and expensive to realize using conventional processingtechniques on semiconductor materials. This feature combined with thelow losses of the substrates and excellent conductivity of the capacitormaterials, will enable high quality factors (Q's) to be realized whichis an important high performance feature of the present invention.

[0131] The MEMS variable capacitor devices 50 are fabricated directly onthe surface of a multi-layer stack of the substrate material 11. Asmentioned previously, a surface preparation is performed prior tofabrication of the MEMS elements. Subsequent to this surfacepreparation, minimum features of 1 to 2 microns can be resolved. Thissurface preparation process and subsequent fabrication ofmicromechanical devices does significantly increase the overall cost ofthe fabrication, and the overall fabrication process will be relativelyinexpensive compared to a processing sequence for semiconductormaterials.

[0132] The packaging of the variable capacitor 50 is accomplished bybonding two pieces of the substrate material 11 and 12 together whereinone of the pieces has the variable capacitor device 50 on the surfaceand the other has a cavity 13 as shown in FIG. 9B and as describedabove. The bonding of substrates 11 abd 12 is performed using eutecticbonding, glass-frit or thermosetting polymers. A hermetic seal can bereadily achieved in this bonding process and the micromechanical devicecan be enclosed in a low-pressure, low humidity environment. A treatmentof the surfaces of the micromechanical device so as to avoidcontamination, as well as reduce likelihood of chemical corrosion can beperformed depending on the design. These surface treatments also help toreduce unwanted stiction effects between the contacting surfaces.Surface treatments are commercially available and have been discussedabove.

[0133] The innovative approach of the present invention for theembodiment of a MEMS-based variable capacitor 50 has many advantages andaddresses the two major challenges in the implementation of a MEMSvariable capacitor device, namely cost and performance. The presentinvention uses a new substrate material that results in a dramaticlowering of cost for materials, as well as processing. By merging thismaterial technology with MEMS, a major performance improvement overcompeting technologies is achieved, thereby enabling a high qualityfactor Q, a high self resonant frequency, and if used with a zipperelectrostatic actuator, a large tuning ratio.

[0134] Another such application of MEMS on LTCC is a MEMS-basedclosed-loop controlled variable capacitor 59 as shown in FIG. 9d. Theembodiment of this device is similar to the discrete variable capacitordiscussed above with the major difference being that the module 11contains an integrated circuit 20, more layers of substrate material 22,and more electrical connections 58. The integrated circuit 20 is animportant part of the closed-loop controlled variable capacitor device59. As discussed above, integrated circuits or ICs can be integratedinto the substrate material with relative ease with this technology. Theintegrated circuit 20 has the ability to accurately measure the actualcapacitance of the variable capacitor 59 over the entire dynamic range,as well as control the level of voltage applied to the electrodes 51driving the actuator 52 so as to achieve closed-loop control of thedesired capacitance value. The relatively high voltages needed to drivethe actuator may be generated on-chip or off-chip, depending on the costand voltage levels of commercially available IC processes. In thepreferred embodiment, flip-chip bonding of the integrated circuit 20 tothe substrate 11 is used as shown in FIG. 9d above. As shown in FIG. 9d,a cavity 60 can be incorporated to encapsulate the IC die 20 and protectit from environmental effects.

[0135] Although the fabrication of the MEMS-based closed-loop controlledvariable capacitor 58 is similar to the MEMS -based variable capacitor55 (in FIG. 9b), there is additional complexity due to the need toprovide for additional layers of substrate material 22 in order to makeelectrical connections 39 to the integrated circuit die 20 and thevariable capacitor device 50, as well as connections from the IC die 20to the outside of the module 18.

[0136] The present invention for the embodiment of a MEMS-basedclosed-loop controlled variable capacitor has many advantages andenables a MEMS variable capacitor device to be integrated with an IC ata low cost while proving excellent performance. Furthermore, the use ofLTCC material in the manner described in the present invention enablesthe MEMS and IC devices to be packaged in a high performance enclosureat a low cost.

[0137] Another embodiment of the present invention is a tunable orswitched inductor 90, as shown in the FIGS. 1OA and 10B. Induction 90 ismade by combining MEMS RF switches 91 and 92 fabricated on the surfaceof a LTCC substrate 31 (See FIG. 3) as described above, with a networkof passive inductors 93 also made on the surface of :LTCC substrate 31.The RF switched networks 91 and 92 placed on the ends of the inductornetwork 93 act to select the desired inductor(s) 94 from the network ofinductors 93. In one embodiment, the inductor values are varied inincrements of 0.5 nH from 1 nH to 10 nH. However, as can be appreciatedby those skilled in the art, any number of variations of the inductorvalues can be made with this invention. The selection of the desiredinductor is made by application of an external electrical signal to thevariable inductor module or package 90. This signal is propagatedthrough the connections made possible through the LTCC multilayeredsubstrate to the RF switch, whereby the device switches to the desiredinductor within the network. The level of voltage or current determinesthe switch setting and the resultant inductor selected. Alternatively,an IC die 36 is packaged in the module 90 (FIG. 1Ob) that receives asignal and determines which switch settings are made to select thedesired inductor 94.

[0138] Packaging is achieved for this system in the manner describedabove whereby the passive inductor network 93 is sealed within layers ofthe device 28, as shown in FIG. 10B. LTCC module 31 and the MEMS RFswitches 95 are enclosed within a cavity 33 formed in an upper LTCCmodule 32. Substrates 31 and 32 are bonded or affixed, as describedabove.

[0139] Fabrication of the MEMS RF switches is performed on the surfaceof a multiplayer stack of LTCC substrates as described in FIGS. 8A-8F.In order to fabricate high-fidelity, high-performance MEMS devices, itis necessary to prepare the LTCC surface in the manner described above.The second switch network 92 is optional. Network 92 can be eliminatedby connecting the outputs of all inductors to the output. If thisswitched inductor system 90 is connected to ground at the output port,this is preferable to lower the losses in the system.

[0140] There are numerous well-known methods of realizing inductors 94in the device layers 28 of LTCC module 31. The approximate inductanceformulas for both planar and 3D inductor geometries is given in thedesign manuals for LTCC processes. More accurate formulas are alsoavailable in the literature. Despite its inherent 3D structure, due torelatively thick LTCC dielectric tapes (see 22 in FIG. 2), it is notfeasible to realize true 3D coils using LTCC. Therefore rectangular, andoctagonal shaped planar spiral inductors are more common. Using suchplanar geometries, inductance values between 1 to 100 nH can be achievedregularly. If higher values of inductance are desired, such planarinductors can be stacked. If stacked inductors are necessary, the groundshields 17 (FIG. 2) that would be used to isolate inductors should beavoided.

[0141] The advantage of the present tunable (or switched) inductor isthat the performance of this device is very high compared to othertechnologies. This is due to the low dielectric losses of the LTCCmaterial and the high performance of the inductors and MEMS switches.Furthermore, the cost of the device of the present invention is veryfavorable.

[0142] Another embodiment of the present invention is a tunableinductor-capacitor (LC) network 100 as shown in the FIGS. 11A and 11B.This device is made by combining a MEMS tunable inductor 102 fabricatedon the surface of an LTCC substrate 31, and as described above, with aMEMS variable capacitor 101, also as described above. Device 100 allowsthe tunability of both the capacitor 101 and inductor 102 values overwide dynamic ranges. Both the tunable capacitor 101 and the tunableinductor 102 are controlled using electrical signals 18 provided throughthe electrical connections made possible with the LTCC substrates 31 and32. Fabrication for both the variable capacitor 101 and the tunableinductor 102, including the RF switches 103, are performed on a stack ofLTCC layers to form a substrates 31, and as described above. Packagingis achieved for the MEMS devices, including the RF switches 103 and thevariable capacitor 101 by bonding or affixing two LTCC substrates 31 and32 as described above wherein one of the LTCC substrates 32 has apreviously formed cavity formed 33 in the bottom surface. The MEMSdevices 101 and 103 are fabricated on the other LTCC substrate 31 andthe two substrates are joined together to enclose the MEMS devices 101and 103 and provide protection to them while simultaneously providingelectrical connections 105.

[0143] As can be appreciated by those skilled in the art, the MEMS-basedtunable LC network 100 can be used as a tunable filter for a variety ofcommunication applications. Integrated circuits, such as ICs 19 and 20in FIG. 2, can be included in the LTCC MEMS-based tunable LC networkmodule 100, as shown in FIG. 11 B, so as to achieve closed-loop controlof the tunable capacitor 101 and selecting the desired inductor 104, orother electrical functionality as desired.

[0144] Yet another application of the present invention is aPhased-Array Antenna as shown in FIG. 12a which illustrates partialcomponents of a complete phased-array antenna system 210 that containsmany sub-array antenna systems 215. A sub-array antenna 215 can, byitself, function as a phased-array antenna; however, it may not meetlink requirements, such as gain to noise temperature (G/T) andequivalent isotropic radiated power (EIRP) unless an equivalent numberof radiating elements are incorporated into the system.

[0145] Although the present invention is described herein with respectto a transmitting antenna, it can also be used with receiving antennasystems, as well. In addition, although the preferred embodiment of theinvention is a single-beam system, those skilled in the art of antennasystems will appreciate that multi-beam antenna systems can be madeusing the fabrication principles of the present invention.

[0146] Referring to FIG. 12a, the sub-array antennas 215 comprisingphased-array antenna system 210 are positioned on a sub-arrayintegration medium 209. Each sub-array antenna 215, in turn, includes aplurality of radiating elements 213. The number of radiating elements213 per sub-array 215 is mainly determined by the manufacturing yield ofa sub-array. With a sufficiently advanced manufacturing capability itwill be possible to fabricate phased-array 210 as a whole system,eliminating the need for integration of sub-arrays 215 using integrationmedium 209.

[0147]FIG. 12c illustrates a three-dimensional perspective of a singleintegrated radiating element 213, while FIG. 13 illustrates across-sectional view of the preferred embodiment of the integratedradiating element 213 of the present invention. Element 213 includes twomultilayer LTCC modules 212 and 214, the layers of which form variouscircuit components, including at least one radiating patch, a polarizercircuit, a power divider or combiner, a band pass filter and verticalinterconnects. The preferred dielectric medium for implementing thesecomponents is low-temperature co-fired ceramic, or LTCC, which allowsmultilayer processing, and thus facilitates the vertical integration andmultilevel electrical connection of the component layers and devices atthe processing stage.

[0148] Although LTCC is the preferred dielectric medium for the presentinvention, it is also possible to use high temperature co-fired ceramic(“HTCC”) for the dielectric medium. The number of circuit elements ineach radiating element 213 depends on the frequency, performance,maximum package size, and system and power distribution requirements ofthe phased-array antenna system. The level of integration depends on thesize of the antenna and complexity of the antenna requirements.

[0149] Radiating element 213 also includes at least one MEMS-basedphase-shifter 215 that is fabricated on LTCC module 212. A four bitphase shifter typically occupies an area of λ/2×λ/2, where λ is thewavelength at the center frequency of operation. If the phase-shifter211 is fabricated in an environment with ε_(eff)=3.0 (where ε_(eff) isthe effective dielectric constant seen by the propagating microwavesignal), a die area of approximately 3.0×3.0 mm² is required.Minimization of the die area is very important to lower the cost of theoverall antenna system, since the packaged phased-shifters are typicallythe most expensive component of such a system. The choice of the numberof bits in phase-shifter 211 will depend on the scanning step, theelement-to-element spacing and the scanning range. Because of therequirements of wide angle scanning, one phase shifter per radiatingelement is needed to avoid the formation of grating lobes.

[0150] The vertical integration benefits of LTCC technology and thelow-loss MEMS switches are crucial for achieving the low-cost,phased-array antenna system 210 of the present invention. Despite recentdevelopments in LTCC processing (for example, photolithographicpatterning of conductor/dielectric layers, zero-shrink processes thatlower the shrinkage in the X-Y plane more than one order of magnitude,and various new dielectric and magnetic layers) the preferred designflow of the present invention employs only techniques currentlyavailable in the mainstream of LTCC processing. However, use of therecent developments in LTCC processing can increase dimensional controland device density, and decrease the volume and reduce the cost offabrication even further.

[0151] The process used to make each radiating element 213 of antennasystem 210 is the same as that shown in FIG. 4. According to the processof the present invention, the two multilayer ceramic modules 212 and 214are formed using the standard LTCC process 40. The standard LTCC processflow is illustrated in FIG. 5. After the surface preparation on themodule 212, MEMS components are formed on the frontside of the module asat step 41 in FIG. 4. And, as at step 42, the ceramic modules 212 and214 are bonded, forming hermetically sealed cavities, in which the MEMScomponents 211 are located. The bonding of modules 212 and 214 can beperformed in a controlled environment to achieve the hermetically sealedcavity: operation in this cavity improves the operation of the MEMSdevices. Finally, after standard processing, as at step 43 in FIG. 4,digital/analog IC chips 220 are preferably flip-chip or wire bonded,just as at step 45 in FIG. 4, to the backside of module 212. Ceramicmodule 212 serves as the integration and packaging medium for ICs 220.At this step, if necessary, thermal spreaders 222 (see FIG. 13) aremounted on ICs 220 as well.

[0152] Ceramic module 212 is the substrate on which the MEMS devices arefabricated, and the other module 214 is the top cover of thehermetically sealed cavity formed by the bonding of modules 212 and 214.From the point of view of the phased-array antenna, the layer 230 thatcontains the MEMS components 211 is nothing more than one of many devicelayers that make up the overall architecture of radiating element 213.This layer, which includes MEMS components and transmission lines, isreferred as the phase-shifter layer 211. Other circuit component layers223-229 are formed in the ceramic modules 212 and 214.

[0153] The two multilayer LTCC modules 212 and 214 forming element 213are formed and fired separately, again using the standard LTCCfabrication process shown in FIG. 5. The patterning of layers isperformed, as at step 110 of FIG. 5. Via holes are opened as at step 112of FIG. 5 and filled as at step 114 with conductor inks. This againallows construction of multiple layers, as at step 116, forming theradiating elements 213 of integrated phased-array antenna 210 in onepackage, as shown in FIG. 13. The process of FIG. 5 again eliminates allthe packaging issues regarding the passive layers such as powerdividers, couplers and radiating elements. It is also possible to obtainlarge numbers of antennas from a single LTCC plate. The LTCC technologyallows the integration and packaging of all the device layers necessaryfor the phased-array antenna 210, except one layer, i.e., thephase-shifter layer 211.

[0154] The phase shifters 211 are fabricated directly on layer 226 ofLTCC module 212. Minimum features (as small as 1 μm) required atphase-shifter 211 are considerably smaller than what can be achieved(>100 μm) by using screen-printing techniques. Therefore, the surface ofbuffer layer 226 must be prepared for photolithography steps. Theminimum feature achievable using lithographic patterning on LTCC with anunprepared surface is about 20 μm. To overcome this limitation, thepresent invention uses special surface preparation techniques, such aschemical-mechanical polishing, combined with thin-film depositiontechnology, photolithography and etching technologies to obtain therequired resolution of microdevices on LTCC layer 226. Phase shifter 211is then packaged when modules 212 and 214 are bonded together and coverlayer 229 in module 214 is placed on top of phase shifter 211.

[0155] Both modules 212 and 214 include numerous vertical connections232 and screen-printed conducting layers 234 between the dielectriclayers 236 comprising each element 213 of antenna 210. The verticalconnections 232 are preferably metal-filled via connections. To minimizecoupling between different device layers, stripline topology ispreferred for the electrical devices 223, 224 and 227 fabricated in theinternal layers of modules 212 and 214. As shown in FIGS. 14a and 14 b,fabricated in the device layers forming each element 213 of phased-arrayantenna 210 are a power divider 223, filters 224, polarizers 227,radiating layers 228 with radiating patches 233 on top of layers 228,and phase-shifters 211. The power divider 223 divides power from asingle power amplifier into many radiating elements in the transmittingantenna or combines received power from several elements. The filters224 minimize the interference from and to other communication bands. Thepolarizers 227 control the polarization of the transmitted/receivedsignals. The radiating layers 228 and radiating patches 233transmit/receive electromagnetic signals, and the phase-shifters 211control the phase-shift for individual radiating elements. In thepreferred embodiment of the invention, the filter and power dividerdevice layers 223 and 224 are formed in the bottom module 212. TheMEMS-based phase-shifter is fabricated on module 212, and the radiatinglayers 228 and patches 233, and polarizer components 227 are in the topmodule 214. Also included in radiating layers 228 are vertical groundshields 237 for shielding between the radiating elements 233/235 in themultiple antennas 210 forming an entire phased-array antenna system.

[0156] It is well known in microwave theory that different devices havedifferent characteristic impedance requirements. For example, atraditional Wilkinson power divider requires a 100 ohm isolationresistor and quarter-wavelength-long transmission lines withcharacteristic impedance of 70.7 ohm. Similarly, branch-line couplersrequire transmission lines with the characteristic impedance of 35.4ohms and termination resistors of 50 ohms. The termination resistors canagain be fabricated either in the internal layers of module 212, such as“buried in” resistors 238 shown in FIG. 13, or located on a surfacewhere they can be trimmed to higher accuracy.

[0157] The screen-printed or photo patterned layers 234 are buried metalpatterns which are used to define interconnections and passive microwavedevices, such as transmission lines, couplers, dividers, etc. Thecharacteristic impedance of the transmission lines is again preferablycontrolled to be in the range of 30 ohms to 100 ohms. This can again bedone by controlling the thickness of the ceramic dielectric layers 236and/or the width of the signal conductor following well known formulasavailable in the literature for variety of transmission lineconfigurations. Preferably, the material system used for dielectriclayers 236 is 943 Green Tape™, which allows the unacceptable losses ofLTCC materials at higher frequencies (20 GHz and above) to be avoided.Using the Dupont 943 material system to form LTCC modules 212 and 214allows low characteristic impedance values (<40 ohm) to be obtained, ifthe signal plane is separated from top and bottom ground planes 239 (forsymmetric stripline configuration) with a single dielectric material.Device layers 223 and 224 shown in FIG. 14a again illustratecross-sectional views of symmetric stripline configurations. Thestripline in 224 consists of three conductive planes: two of them groundplanes 239 and a signal plane 243 in the middle. Vertical connections244 and 247 connects signal planes 243 from one device to another one bygoing through the ground planes. As can be seen, two dielectric tapelayers 236 are used to separate the signal plane 243 from ground planes239. Based-on the limitations on minimum patternable conductor width,high impedance values (>60 ohms) may require more than one LTCC layer onboth sides of signal plane 243. If the minimum line width is around 100μm, then two dielectric layers 236 have to be used on both sides ofsignal plane 243.

[0158] As shown in FIG. 13, in the preferred embodiment of the inventioneach of the microwave device layers 223 and 224 in module 212 is formedusing four layers of 943 dielectric tape 236. Of course, the number oflayers needed would change if a different dielectric with differentproperties and thicknesses were used.

[0159] A stripline transmission line configuration is preferable for thevertical connections 232, because ground planes 239 on both sides of thestripline circuits help minimize the interference between circuits inthe different layers 223, 224 and 227. Therefore, the electromagneticisolation between the vertical circuits is easier to achieve. Inaddition, the stripline configuration has a homogeneous dielectricmedium, which lowers signal dispersion.

[0160] Other transmission line configurations, such as shielded-coplanartransmission lines, can be used in the internal device layers 223, 224and 227. At outer surfaces, variations of microstrip and coplanarconfigurations can be used. For the MEMS device layer 230, aconductor-backed coplanar configuration is preferable.

[0161] All the vertical connections 232, 233, 237 and 247 shown in FIG.13 are the same. However, functionally, there are important differences.Vertical connections between the ground planes are not that critical forsignal integrity. On the other hand, connections between the signalplanes are understandably more important. Vertical connections 232 areground connections for module 212, whereas vertical connections 233 aresignal connections for module 214 in FIG. 13. The shielding for verticalconnections is important if they originate from a signal plane. Thus,the vertical connections between two layers of devices 223, 224, and/or227 can be unshielded or shielded coaxial-type connections. In bothcases, the vertical connections 232 have to be designed carefully tominimize the internal reflections and losses between two layers ofdevices 223, 224, and/or 227.

[0162] Vertical connections 242 can be also used to shieldelectromagnetic interference and coupling. If there are multiplecomponents in a single layer, grounded-vertical connections 242 placedbetween them will lower interference significantly. For example, lookingat the bottom side 240 of module 212, integrated circuits 220 placed inthe LTCC cavity 241 need to be isolated from other device layers such as223 and 224. Vertical connections 242 embedded in the sidewalls ofcavity 241 are grounded to minimize electromagnetic radiation tointernal device layers, such as 223 and 224.

[0163] To maintain proper operation, ICs 220 can be flip-chip bonded tomodule 212. Copper thermal spreaders 222 can then be mounted directly onthe backside of ICs 220, if necessary. If IC power consumption is not anissue, then low-cost wire-bonding techniques can be employed to mountlow pin-count ICs 220 on module 212. Integrated circuit 220 can be anyof the following: a control circuit for the MEMS phase-shiftercomponents, a power module for such MEMS components, a microprocessor ora signal processor, a high frequency power amplifier, a high frequencylow noise amplifier, high frequency down-converters, or any otheranalog/digital integrated circuits that are necessary for the operationof the phased-array system.

[0164] Where IC 220 in FIG. 13 is a power amplifier or a low noiseamplifier (“LNA”), vertical connections can be used to isolate thesedevices, since they can potentially interfere with many circuit devicesin radiating element 213, if special precautions are not taken. Thus,vertical connections 242 limit the interference from such ICs in thehorizontal direction, whereas ground planes 239 blocks signals in thevertical direction. Such shielding measures are not necessary for lowfrequency and low power IC chips like logic, memory and DSP blocks.

[0165] But not every radiating element 213 requires an amplifier. Themost basic advantage of the technology of the present invention is thatthe losses are so low that the number of amplifiers necessary to achievea function can be reduced significantly, thereby also resulting insignificant decreases in system complexity and cost with correspondingincreases in system reliability. In the present invention, the size ofsub-array 215 (i.e., the number of radiating elements 213 in a sub-array215) depends on the output power level of an amplifier IC 220 and theloss of each element 213. It is possible that a single amplifier IC 220can support 4×4=16 elements 213. In that case, a logical choice for thesize of sub-array 215 would be 4×4=16 elements 213. If a power amplifier220 can support twenty-five elements 213, the a logical choice for thesize of sub-array 215 would be 5×5=25 radiating elements 213. Therefore,ideally, there is one amplifier 220 per sub-array 215. In the devicelayers 223 or 224 (FIG. 13), this power is divided for individualelements equally, and in layers above, including in phase shifter layer230, the signal is processed independently in each element 213.Eventually, they are radiated via patch 235 with a certain polarizationcharacteristic and time delay. It is the time delay that is introducedto the signal to the signal as it propagates to the radiating elementand the subsequent inference of the radiated electromagnetic signal frommultiple radiating elements that provides the scanning capability of thephased-array antenna 210. The phase shifter layer 230 is where a timedelay is introduced to the signal prior to reaching the radiatingelement.

[0166] As illustrated in FIG. 14a, lower module 212 has three distinctfunctional areas, i.e., an interconnection layer 225, two device layers223 and 224, and a buffer layer 226. The interconnection layer 226 isused to interconnect through connections 244 and 246 different ICs 220and lumped components such as inductors, capacitors, and resistors 238,either discrete or formed in or on module 212. The device layers 223 and224 are distributed or lumped, as necessary, for phased-array operation.They are connected together by a connection 247 extending between suchlayers. Several device layers can be integrated vertically in thissection.

[0167] The buffer layer 226 is used only for connection, through avertical connection 248, to the MEMS phase-shifters 211, which areformed on top of this layer. Since the front surface 264 of layer 226 ispolished prior to the fabrication of the MEMS devices 211 on top oflayer 226, no surface conductors are printed prior to polishing. In thepreferred process flow, LTCC compatible bonding materials are printedand fired after polishing. However, it is possible to have oneun-patterned conductor layer, which is deposited as a part of the LTCCprocess. In this case, the surface preparation would include metalpolishing rather than ceramic polishing, and the MEMS process sequenceshown in FIG. 4 must be modified accordingly.

[0168] The second module 214, as shown in FIG. 14b, also has threefunctional layers, i.e., a MEMS cover layer 229, at least one devicelayer 227, and a radiation layer 228. The MEMS cover layer 229 includesa cavity 251 for the MEMS phase-shifters 211 that enables properpackaging of the MEMS devices 211 fabricated on module 212. The devicelayer 227 is one or more layers of passive devices. One or moresignal-feed ports 252 can be used to feed the radiating patch 235. Twoports 252 are shown in FIG. 14b. Also the bandwidth of the radiation canbe improved by adding a second radiating patch (not shown) on top ofmain patch 235 in FIG. 14b. Typically, this second patch improves theradiation properties of the main patch by allowing better match at theinput at ports 252. If the signals are 90 degrees out of phase betweenthe input ports, this would generate a circularly polarized radiation,Again radiation properties can be changed by changing the number ofports, location of the ports, the relative phase difference between theports and the patch pattern. These variations are well-documented in theantenna design literature and can be applied to the design of thepresent invention.

[0169] Surface preparation for buffer layer 226, which acts as asubstrate for the fabrication of MEMS devices 211, can potentiallyinclude multiple steps such as planarization of ceramic parts,planarization of first metallization, and deposition of bondingmaterials. The last two items are optional because it is obvious tothose skilled in the art of hermetic packaging and MEMS fabrication thatthere are many different ways to achieve the desired hermetically sealedcavity formed by the bonding of the two ceramic modules 212 and 214.

[0170] Surface planarization is necessary prior to MEMS fabrication dueto large surface roughness of fired ceramic parts. Such planarizationwould be performed in a manner like that described above with respect tothe other MEMS devices. Another optional step, which can be done as apart of surface preparation, is the deposition of bonding materials onthe surface of buffer layer 226 prior to MEMS processing, as discussedabove. Once the surface preparation is completed, the MEMS fabricationprocess is done using various MEMS process flows, such as that shown inFIGS. 8A-8F.

[0171] At system level, several well-known phase-shifter topologies canbe used to form the phase-shifters 211 using MEMS switches and/or MEMStunable capacitors. It is well know in the art that many topologies ofMEMS switches can be used as tunable capacitors, if the applied voltageis kept below the actuation voltage. At low frequencies (<10 GHz),usually phase-shifters that employ variable (tunable) capacitors andinductors are used. Other topologies tend to have very large areas. Onthe other hand, at high frequencies (>10 GHz), switched-delay-line,loaded-line or reflection topologies are preferred. All thesephase-shifter architectures can be built on module 212 as long as thenecessary MEMS components can be built in the MEMS process of choice.

[0172] The MEMS-based phase-shifter 211 used in the antenna 210 of thepresent invention is preferably based on switched delay lines (notshown). The MEMS delay lines use a conductor-backed coplanar design toobtain good isolation from the other device layers. By using a thickmetal conductor, losses are minimized. Total attenuation for theconductor and dielectric in the transmission lines is 1 dB/cm at 30 GHz.If 10 μm thick silver strips are used on the 943 Green Tape, losses aslow as 0.2 dB/cm at 30 GHz can be obtained.

[0173] In the switched-delay line approach, the cost varies considerablywith the fabrication technology. One of the reasons for this variationis that, while the system area remains almost the same, themanufacturing cost per unit area changes drastically. For example, GaAssubstrates are about one order of magnitude more expensive thanhigh-quality, non-crystalline, microwave substrates. Since themechanical operation of MEMS switches does not depend on the type of thesubstrate on which they are fabricated, they can be fabricated on anysubstrates having sufficiently low dielectric losses at the operationalfrequencies, including 450×450 mm large LTCC panels, as opposed tocostly 100 mm or 150 mm GaAs substrates. In addition, at least sevenmasks with features as small as 0.7 um are necessary for MonolithicMicrowave Integrated Circuit (“MMIC”)-based phase-shifters. Not onlydoes GaAs processing require more steps, but also each processing stepis more expensive to perform. This is especially true of an MMIC processwith ground vias, which are necessary for low noise operation and whichincrease the unit area cost of GaAs substantially. On the other hand,ground vias are readily available in LTCC panels. The number of masksnecessary for device fabrication is 4-6 and the minimum feature isaround 1.0 um.

[0174] To prevent stiction between contact surfaces of MEMS switch, andto maintain low-resistance contacts in switches, surface treatments arenecessary to avoid contamination and unwanted chemical reactions, suchas oxidation. Commercially available anti-stiction coatings, such as thedichlorodimethylsilane (DDMS) monolayer, the octadecyltrichlorosilane(OTS) self-assembled monolayer, or similar products can be used on themetal surfaces to minimize any unintentional adhesion in mechanicalswitches or other contacting or near-contacting surfaces within thepresent invention.

[0175] The MEMS processing can be performed on large-area-processing(LAP) equipment (not shown). This equipment, like LTCC processing tools,can handle very large panels (or wafers). The current generation of theLAP tools has the capability of processing panels larger than 800×800 mmand capable of handling minimum features as small as 2 μm or less. Onthe other hand, current generation of LTCC manufacturing tools canprocess only 200×200 mm panels, though it is straightforward for sizesto 800×800 mm and beyond.

[0176] The MEMS fabrication is followed by the bonding of the two LTCCmodules 212 and 214 at low pressure and in a low-humidity environment.If other bonding techniques were used, the necessary surface preparationwould precede the selected bonding process. The bonding of modules 212and 214 is then followed by the integration of ICs 220 and otherdiscrete components (not shown) on the backside of module 212 (see FIG.13). For this purpose, flip-chip bonding is more reliable andrepeatable, and lends itself to better thermal management options, asdescribed below. Therefore, especially high-power, high-frequency ICs220 are preferably flip-chip bonded in shielded cavities 241 in module212 to minimize the electromagnetic coupling to other sensitive circuitsand to achieve better heat removal from the backside of ICs 220. ICs 220can be analog or digital ICs, MMICs and/or Radio Frequency IntegratedCircuits (“RFICs”).

[0177] The quality of flip-chip bonds are assessed by determining thedetuning of the circuits due to their proximity to ceramic module 212,the reflection due to transition, and the insertion loss at eachconnection. Typically, the size of the pads 268 (seen in FIG. 14a) andthe metal extensions are preferably selected to be as small as possibleto minimize parasitic capacitances. The height of the pads 268 istypically chosen to be larger than one third of ground-to-ground spacingon the 50ΩQ CPW lines on chip to minimize the detuning. By carefulplacement of contact pads 268, and if necessary, inductive compensation,a return loss above 25 dB at 40 GHz and an insertion loss of less than0.25 dB can be achieved.

[0178] Dupont 943 dielectric tape has thermal conductivity of ˜5 W/mK.This conductivity can be further improved by using conductor-filledthermal vias 232. It has been shown that with proper thermal design, itis possible to obtain thermal conductivities close to those of costlyBeryllium Oxide (“BeO”) and Aluminum Nitride (“AIN”) (>250W/mK)substrates. Here, thermal spreaders 222 are mounted on the backside ofthe flip-chip bonded ICs 220. If the depth of the cavity 241 is the sameas the thickness of ICs 220, the thermal spreader 222 will function asan electromagnetic shield too.

[0179] Similarly, other front end components can be improved using MEMScomponents embedded in LTCC as well, including radiating patches.Although patch 235 described herein is fixed in size, the presentinvention allows the alteration of the physical shape of the radiatingpatch seen by electromagnetic signals. RF filters (constructed based onLC networks shown in FIG. 11a) benefit from the technology in thepresent invention as well. For example, extremely functional filters canbe realized on LTCC whereby the filtering characteristics can be alteredas desired under electronic control,. Voltage controlled oscillatorswould benefit from this technology, because it would provide excellenttunable capacitors and inductors in the same package. Mixers are theremaining critical component in the front-end of communication networks.Significant functionality increases can be achieved for the mixers aswell using the present invention.

[0180] Although the present invention has been described in terms of aparticular embodiment and process, it is not intended that the inventionbe limited to that embodiment. Modifications of the embodiment andprocess within the spirit of the invention will be apparent to thoseskilled in the art. The scope of the invention is defined by the claimsthat follow.

What is claimed is:
 1. A radio frequency device compromising: a firstsubstrate comprised of a first plurality of low-temperature co-firedceramic (“LTCC”) layers forming a first circuit used in the operation ofthe device, a second substrate comprised of a second plurality of LTCClayers forming a second circuit used in the operation of the device, andat least one microelectromechanical (“MEMS”) device between the firstand second substrates, wherein the second substrate is bonded to thefirst substrate so as to enclose the at least one MEMS device betweenthe first and second substrates.
 2. The radio frequency device recitedin claim 1, wherein the second substrate is bonded to the firstsubstrate to form a hermetically sealed chamber containing the at leastone MEMS device.
 3. The radio frequency device recited in claim 1further comprising a plurality of vertical interconnects extendingthrough and interconnecting the first and second pluralities of LTCClayers comprising the first and second substrates.
 4. The radiofrequency device recited in claim 1 wherein the first plurality of LTCClayers comprising the first substrate includes a buffer layer that is asubstrate on which the at least one MEMS device is fabricated.
 5. Theradio frequency device recited in claim 1 further comprising at leastone integrated circuit (“IC”) bonded to the first substrate.
 6. Theradio frequency device recited in claim 5 wherein the first plurality ofLTCC layers includes an interconnect layer through which the at leastone integrated circuit is connected to the first substrate.
 7. The radiofrequency device recited in claim 1 further comprising a plurality ofdiscrete components buried-in the first plurality of LTCC layers.
 8. Theradio frequency device recited in claim 7 wherein the plurality ofburied-in discrete components includes components resistors, capacitorsand/or inductors.
 9. The radio frequency device recited in claim 1wherein the first and second pluralities of LTCC layers each include atleast one passive microwave device selected from the group consisting oftransmission lines, couplers and dividers.
 10. The radio frequencydevice recited in claim 5 wherein the first plurality of LTCC layersincludes a cavity in which the at least one integrated circuit is bondedto the first plurality of LTCC layers.
 11. The radio frequency devicerecited in claim 5 wherein the at least one integrated circuit includesat least one circuit from the group consisting of low-frequencyanalog/digital ICs, MMICS, and RFICs.
 12. The radio frequency devicerecited in claim 5 wherein the at least one integrated circuit includesat least one circuit from the group consisting of a control circuit forthe MEMS device, a power module for the MEMS device, a microprocessor, asignal processor, a high frequency power amplifier, a high frequency lownoise amplifier, and high frequency up and down converters.
 13. Theradio frequency device recited in claim 5 wherein the second pluralityof LTCC layers further comprises includes a ground shielding extendingthrough the second plurality of LTCC layers to shield the at least oneMEMS device or IC from radiating components in other layers.
 14. Theradio frequency device recited in claim 1 wherein the first and secondpluralities of LTCC layers include ground planes for shielding the firstand second circuits.
 15. The radio frequency device recited in claim 4wherein the buffer layer is comprised of a plurality of layers.
 16. Theradio frequency device recited in claim 5 wherein the integratedcircuits are flip-chip bonded to screen-printed surface metal patternson a layer of the first plurality of LTCC layers.
 17. The radiofrequency device recited in claim 5 wherein the integrated circuits arewire-bonded to screen-printed surface metal patterns on a layer of thefirst plurality of LTCC layers.
 18. The radio frequency device recitedin claim 5 wherein the integrated circuits are flip-chip bonded tophoto-patterned surface metal patterns on a layer of the first pluralityof LTCC layers.
 19. The radio frequency device recited in claim 5wherein the integrated circuits are wire-bonded to photo-patternedsurface metal patterns on a layer of the first plurality of LTCC layers.20. A radio frequency system compromising: at least onemicroelectromechanical (“MEMS”) device, at least a first plurality ofLTCC layers forming at least one first circuit used in the operation ofthe MEMS device, at least a second plurality of LTCC layers forming atleast one second circuit used in the operation of the MEMS device, theMEMS device being formed between the first and second pluralities ofLTCC layers, the second plurality of LTCC layers being bonded to thefirst plurality of LTCC layers whereby the MEMS device is enclosedbetween the first and second pluralities of LTCC layers.
 21. The radiofrequency system recited in claim 20 wherein the second plurality ofLTCC layers is bonded to the first plurality of LTCC layers to form ahermetically sealed chamber containing the at least one MEMS device. 22.The radio frequency system recited in claim 20 wherein the firstplurality of LTCC layers includes a buffer layer that serves as asubstrate on which the at least one MEMS device is fabricated.
 23. Theradio frequency system recited in claim 20 further comprising at leastone integrated circuit bonded to the first plurality of LTCC layers. 24.The radio frequency system recited in claim 23 further comprising aplurality of integrated circuits including at least one circuit selectedfrom the group consisting of low-frequency analog/digital ICs, MMICs,and RFICs.
 25. The radio frequency system recited in claim 23 furthercomprising a plurality of integrated circuits including at least onecircuit selected from the group consisting of a control circuit for theMEMS device, a power module for the MEMS device, a microprocessor, asignal processor, a high frequency power amplifier, a high frequency lownoise amplifier, high frequency down-converters.
 26. A MEMS devicecomprising: a first ceramic module formed from of a first plurality ofdielectric layers, the first plurality of dielectric layers including atleast one first circuit layer; a second ceramic module formed from of asecond plurality of dielectric layers, the second plurality ofdielectric layers including at least one second circuit layer, a layerbetween the first and second ceramic modules including at least onemicroelectromechanical (“MEMS”) switch forming at least onephase-shifter, the second ceramic module being bonded to the firstceramic module to thereby form a cavity in which the MEMS switch islocated.
 27. The MEMS device of claim 26, wherein the ceramic modulesare formed using an LTCC process.
 28. The MEMS device of claim 26,wherein the ceramic modules are formed using an HTCC process.
 29. TheMEMS device of claim 27, wherein the ceramic modules are formed from 943Green Tape™.
 30. A MEMS device comprising: a first ceramic module formedfrom of a first plurality of dielectric layers, the first plurality ofdielectric layers including at least one first circuit layer, a bufferlayer, and a plurality of interconnections between the at least onefirst circuit layer and the buffer layer; a second ceramic module formedfrom of a second plurality of dielectric layers, the second plurality ofdielectric layers including at least one second circuit layer, a coverlayer, a plurality of radiation layers, and a plurality ofinterconnections between the second circuit layer, cover layer, andradiation layers; and a layer between the first and second ceramicmodules including at least one microelectromechanical switch forming atleast one phase-shifter.
 31. The MEMS device of claim 30 furthercomprising a plurality of integrated circuits mounted on the firstceramic module, and wherein the first plurality of dielectric layersfurther includes a plurality of interconnecting layers for connectingthe integrated circuits to the dielectric layers forming the first andsecond ceramic modules.
 32. The MEMS device of claim 30, wherein theceramic modules are formed using an LTCC process.
 33. The MEMS device ofclaim 30, wherein the ceramic modules are formed using an HTCC process.34. A MEMS device comprising: a first ceramic module formed from of afirst plurality of dielectric layers, the first plurality of dielectriclayers including at least one first circuit layer; a second ceramicmodule formed from of a second plurality of dielectric layers, thesecond plurality of dielectric layers including at least one secondcircuit layer, a layer between the first and second ceramic modulesincluding at least one microelectromechanical (“MEMS”) switch, thesecond ceramic module being bonded to the first ceramic module, tothereby form a cavity in which the MEMS switch is located, a pluralityof integrated circuits mounted on the first ceramic module, a pluralityof interconnecting layers extending through the first plurality ofdielectric layers for connecting the integrated circuits to thedielectric layers forming the first and second ceramic modules, and aplurality of discrete components buried-in the first and secondpluralities of dielectric layers.
 35. The MEMS device of claim 34,wherein the ceramic modules are formed using an LTCC process.
 36. TheMEMS device of claim 35, wherein the ceramic modules are formed from 943Green Tape™.
 37. The MEMS device of claim 34, wherein the ceramicmodules are formed using an HTCC process.
 38. An electrical devicecomprising: a first ceramic module formed from of a first plurality ofdielectric layers, the first plurality of dielectric layers including atleast one first circuit layer, a buffer layer, and a plurality ofinterconnections between the at least one circuit layer and the bufferlayer; a second ceramic module formed from of a second plurality ofdielectric layers, the second plurality of dielectric layers includingat least one second circuit layer, a cover layer, and a plurality ofinterconnections between the second circuit layer and the cover layer;and a layer formed between the first and second ceramic modulesincluding at least one microelectromechanical (“MEMS”) switch.
 39. Theelectrical device of claim 38 further comprising a plurality ofintegrated circuits mounted on the first ceramic module, the firstplurality of dielectric layers further including interconnecting layersfor connecting the integrated circuits to the dielectric layers formingthe first and second ceramic modules.
 40. The electrical device recitedin claim 39 wherein the plurality of integrated circuits includes atleast one circuit selected from the group consisting of low-frequencyanalog/digital ICs, MMICs, and RFICs.
 41. The electrical device recitedin claim 39 wherein the plurality of integrated circuits includes atleast one circuit selected from the group consisting of a controlcircuit for the electrical device, a power module for the electricaldevice, a microprocessor, a signal processor, a high frequency poweramplifier, a high frequency low noise amplifier, a high frequencydown-converter.
 42. The electrical device of claim 38, wherein theceramic modules are formed using an LTCC process.
 43. The electricaldevice of claim 38, wherein the ceramic modules are formed using an HTCCprocess.
 44. A radio frequency device compromising: a first substratecomprised of a first plurality of low-temperature co-fired ceramic(“LTCC”) layers, a second substrate comprised of a second plurality ofLTCC layers, and at least one microelectromechanical (“MEMS”) devicebetween the first and second substrates, wherein the second substrate isbonded to the first substrate so as to enclose the at least one MEMSdevice between the first and second substrates.
 45. The radio frequencydevice as recited in claim 44 wherein said device is a tunablecapacitor.
 46. The radio frequency device as recited in claim 44 whereinsaid device is an attenuator.
 47. The radio frequency device as recitedin claim 44 wherein said device is a filter.
 48. The radio frequencydevice as recited in claim 44 wherein said device is a reconfigurableantenna.
 49. The radio frequency device as recited in claim 44 whereinsaid device is a reconfigurable power amplifier.
 50. The radio frequencydevice as recited in claim 44 wherein said device is a low-noiseamplifier.
 51. The radio frequency device as recited in claim 44 whereinsaid device is a variable controlled oscillator.
 52. The radio frequencydevice as recited in claim 44 wherein said device is a mixer.
 53. Theradio frequency device as recited in claim 44 wherein said device is avariable capacitor.
 54. The MEMS device of claim 27, wherein the ceramicmodules are formed from 951 Green Tape™.
 55. The MEMS device of claim35, wherein the ceramic modules are formed from 951 Green Tape™.
 56. Amethod of forming a radio frequency (“RF”) device including at least oneMEMS device comprising the steps of: fabricating a first module from afirst plurality of low-temperature co-fired ceramic (“LTCC”) layers, thefirst plurality of layers forming at least a first circuit used in theoperation of the MEMS device; fabricating a second module from a secondplurality of low-temperature co-fired ceramic (“LTCC”) layers, thesecond plurality of layers forming at least a second circuit used in theoperation of the MEMS device; polishing a surface of a front layer ofthe first module to be used as a substrate after fabrication of thefirst module is completed; fabricating on the front layer the at leastone MEMS device using MEMS processing; and bonding the first and secondmodules together to thereby form a cavity containing the at least oneMEMS device.
 57. The method of forming a RF device as recited in claim56 further comprising the steps of polishing a surface of a back layerof the second module to be used as a cover after fabrication of thesecond module is completed and applying two-component brazing materialson the front and back layers prior to bonding the first and secondmodules together.
 58. The method of forming a RF device as recited inclaim 56 wherein the step of bonding the first and second modulestogether is performed using eutectic bonding.
 59. The method of forminga RF device as recited in claim 56 wherein the step of bonding the firstand second modules together is performed using an insulating layer suchas glass-frit.
 60. The method of forming a RF device as recited in claim56 wherein the step of bonding the first and second modules together isperformed using an insulating layers such as a thermalsetting polyimidefilm.
 61. The method of forming a RF device as recited in claim 56wherein the step of applying two-component brazing materials on thefront and back layers comprises the steps of: depositing a plurality offirst contact pads on a front layer of the first module; planarizing thefront layer of the first module; depositing an adhesion layer and asoldering conductor on the first contact pads; firing the first moduleat a temperature greater than 800° C.; depositing a plurality of secondcontact pads on a back layer of the second module; planarizing the backlayer of the second module; depositing an adhesion layer and a solderingconductor on the second contact pads; and firing the first module at atemperature greater than 800° C.
 62. The method of forming a RF deviceas recited in claim 56 wherein the step of polishing the surfaces of thefront and back layers is performed using a mechanical orchemical/mechanical polish.
 63. The method of forming a RF device asrecited in claim 57 wherein the step of polishing the surfaces of thefront and back layers is performed using a mechanical orchemical/mechanical polish.
 64. The method of forming a RF device asrecited in claim 56 wherein the step of bonding the first and secondmodules together is performed at low pressure and in a low-humidityenvironment.
 65. The method of forming a RF device as recited in claim56 wherein the step of bonding the first and second modules together isperformed in an inert gas atmosphere.
 66. The method of forming a RFdevice as recited in claim 56 wherein the first and second modules arebonded together to thereby form a hermetically sealed cavity containingthe at least one MEMS device.
 67. The method of forming a RF device asrecited in claim 56 wherein the step of fabricating the MEMS devicecomprises forming a switch.
 68. The method of forming a RF device asrecited in claim 56 further comprising the step of forming verticalinterconnects extending through the first and second pluralities of LTCClayers.
 69. The method of forming a RF device as recited in claim 56further comprising the step of forming in the first plurality of LTCClayers a buffer layer that is a substrate on which the at least one MEMSdevice is fabricated.
 70. The method of forming a RF device as recitedin claim 56 further comprising the step of bonding to one of the firstplurality of LTCC layers at least one integrated circuit.
 71. The methodof forming a RF device as recited in claim 70 further comprising thestep of forming in the first plurality of LTCC layers an interconnectlayer for interconnecting the integrated circuit to the MEMS device. 72.The method of forming a RF device as recited in claim 56 furthercomprising the step of fabricating in the first plurality of LTCC layersa plurality of buried-in discrete components.
 73. The method of forminga RF device as recited in claim 72 wherein the discrete componentsinclude at least one device from the group consisting of resistors,capacitors and inductors.
 74. The method of forming a RF device asrecited in claim 56 further comprising the step of forming in the firstand second pluralities of LTCC layers screen-printed buried metalpatterns that are used to define interconnections and passive microwavedevices.
 75. The method of forming a RF device as recited in claim 74wherein the passive microwave devices include at least one device fromthe group consisting of transmission lines, couplers, and dividers. 76.The method of forming a RF device as recited in claim 56 furthercomprising the step of forming in the first and second pluralities ofLTCC layers photo-patterned buried metal patterns that are used todefine interconnections and passive microwave devices.
 77. The method offorming a RF device as recited in claim 76 wherein the passive microwavedevices include at least one device from the group consisting oftransmission lines, couplers, and dividers.
 78. The method of forming aRF device as recited in claim 56 further comprising the step of formingin the second plurality of LTCC layers ground shielding extendingthrough said layers to shield the at least one MEMS device fromradiating.
 79. The method of forming a RF device as recited in claim 70further comprising the step of flip-chip bonding the integrated circuitsto screen-printed surface metal patterns on a layer of the firstplurality of LTCC layers.
 80. The method of forming a RF device asrecited in claim 70 further comprising the step of wire-bonding theintegrated circuits to screen-printed surface metal patterns on a layerof the first plurality of LTCC layers.
 81. The method of forming a RFdevice as recited in claim 70 further comprising the step of flip-chipbonding the integrated circuits to photo-patterned surface metalpatterns on a layer of the first plurality of LTCC layers.
 82. Themethod of forming a RF device as recited in claim 70 further comprisingthe step of wire-bonding the integrated circuits to photo-patternedsurface metal patterns on a layer of the first plurality of LTCC layers.83. The method of forming a RF device as recited in claim 56 wherein theMEMS process is performed in large-area-processing tools or standardsemiconductor tools.
 84. A method of forming an electrical devicecomprising the steps of: fabricating a first module from a firstplurality of low-temperature co-fired ceramic (“LTCC”) layers, the firstplurality of layers forming at least a first circuit used in theoperation of the electrical device; fabricating a second module from asecond plurality of low-temperature co-fired ceramic (“LTCC”) layers,the second plurality of layers forming at least a second circuit used inthe operation of the electrical device; polishing a surface of a frontlayer of the first module to be used as a substrate after fabrication ofthe first module is completed; fabricating on the front layer at leastone microelectromechanical device (“MEMS”) using standard MEMSprocessing; and bonding the first and second modules together to therebyform a cavity containing the at least one MEMS device.
 85. The method offorming an MEMS device as recited in claim 84 further comprising thesteps of polishing a surface of a back layer of the second module to beused as a cover after fabrication of the second module is completed andapplying two-component brazing materials on the front and back layersprior to bonding the first and second modules together.
 86. The methodof forming a MEMS device as recited in claim 84 wherein the step ofbonding the first and second modules together is performed usingeutectic bonding.
 87. The method of forming a MEMS device as recited inclaim 84 wherein the step of bonding the first and second modulestogether is performed using an insulating layer such as glass-frit. 88.The method of forming a MEMS device as recited in claim 84 wherein thestep of bonding the first and second modules together is performed usingan insulating layers such as a thermal setting polyimide film.
 89. Themethod of forming an electrical device as recited in claim 84 whereinthe step of applying two-component brazing materials on the front andback layers comprises the steps of: depositing a plurality of firstcontact pads on a front layer of the first module; planarizing the frontlayer of the first module; depositing an adhesion layer and a solderingconductor on the first contact pads; firing the first module at atemperature greater than 800° C.; depositing a plurality of secondcontact pads on a back layer of the second module; planarizing the backlayer of the second module; depositing an adhesion layer and a solderingconductor on the second contact pads; and firing the first module at atemperature greater than 800° C.
 90. The method of forming an electricaldevice as recited in claim 84 wherein the step of polishing surfaces ofthe front and back layers is performed using a mechanical orchemical/mechanical polish.
 91. The method of forming an electricaldevice as recited in claim 84 wherein the step of bonding the first andsecond modules together is performed at low pressure and in alow-humidity environment.
 92. The method of forming an electrical deviceas recited in claim 84 wherein the first and second modules are bondedtogether to thereby form a hermetically sealed cavity containing the atleast one MEMS device.
 93. The method of forming an electrical device asrecited in claim 84 further comprising the step of forming verticalinterconnects extending through the first and second pluralities of LTCClayers.
 94. The method of forming an electrical device as recited inclaim 84 further comprising the step of bonding to one of the firstplurality of LTCC layers at least one integrated circuit.
 95. The methodof forming an electrical device as recited in claim 94 furthercomprising the step of forming in the first plurality of LTCC layers aninterconnect layer for interconnecting the integrated circuit to theelectrical device.
 96. The method of forming an electrical device asrecited in claim 84 further comprising the step of fabricating in thefirst plurality of LTCC layers a plurality of buried-in discretecomponents.
 97. The method of forming an electrical device as recited inclaim 93 wherein the vertical interconnects are metal-filled vias. 98.The method of forming an electrical device as recited in claim 84wherein the MEMS process is performed in large-area-processing tools orstandard semiconductor tools.
 99. A device which operates at radiofrequencies compromising: at least one microelectromechanical (“MEMS”)variable capacitor, a first substrate on which the MEMS variablecapacitor is fabricated, the first substrate being comprised of a firstplurality of low-temperature co-fired ceramic (“LTCC”) layers forming afirst circuit used in the operation of the device, and a secondsubstrate comprised of a second plurality of LTCC layers forming atleast a second circuit used in the operation of the device; and whereinthe second substrate is bonded to the first substrate so as to enclosethe MEMS variable capacitor between the first and second substrates.100. The device recited in claim 99 wherein the second substrate isbonded to the first substrate to form a hermetically sealed chambercontaining the MEMS variable capacitor.
 101. The device recited in claim99 wherein the first and second pluralities of LTCC layers comprisingthe first and second substrates are interconnected by verticalinterconnects extending through the layers.
 102. The device recited inclaim 99 wherein the first plurality of LTCC layers comprising the firstsubstrate includes a buffer layer that serves as a substrate on whichthe MEMS variable capacitor is fabricated.
 103. The device recited inclaim 99 wherein the variable capacitor includes a movable electrode andwherein applied electrostatic actuation voltage deflects the movableelectrode to thereby change the capacitance of the variable capacitor.104. The device recited in claim 99 wherein the variable capacitorincludes shaped electrodes whereby the relationship between the appliedelectrostatic actuation voltage and the capacitance of the variablecapacitor is linear.
 105. The device recited in claim 103 wherein thevariable capacitor includes mechanical barriers to stop the deflectionof the movable electrode at a predefined position to thereby set thetuning range of the device.
 106. The device recited in claim 103 whereinthe variable capacitor includes non-linear springs that provide anon-linear mechanical restoring force to the movable electrode so as tocompensate for non-linearity in the applied electrostatic actuationvoltage.
 107. The device recited in claim 103 wherein the variablecapacitor includes at least four electrodes so to provide for a two-portdevice and thereby de-couple the capacitance of the device from theactuation of said device.
 108. The device recited in claim 99 furthercomprising at least one integrated circuit bonded to the firstsubstrate.
 109. The device recited in claim 108 wherein the firstplurality of LTCC layers includes an interconnect layer through whichthe at least one integrated circuit is connected to the first substrate.110. The device recited in claim 99 wherein the first plurality of LTCClayers includes a plurality of discrete components buried-in saidlayers.
 111. The device recited in claim 110 wherein the first pluralityof buried-in discrete components contains at least one component fromthe group consisting of is resistors, capacitors and inductors.
 112. Thedevice recited in claim 99 wherein the first and second pluralities ofLTCC layers include at least one passive microwave device from the groupconsisting of transmission lines, couplers and dividers.
 113. The devicerecited in claim 108 wherein the first plurality of LTCC layers includesa cavity in which the integrated circuits are bonded to the firstplurality of LTCC layers.
 114. The device recited in claim 113 whereinthe integrated circuits include at least one circuit from a groupconsisting of low-frequency analog/digital ICs, MMICS, and RFICs. 115.The device recited in claim 1 13 wherein the integrated circuits includeat least one circuit from a group consisting of a control circuit forthe MEMS capacitor, a power module for the MEMS capacitor, amicroprocessor, a signal processor, a high frequency power amplifier, ahigh frequency low noise amplifier, high frequency up and downconverters.
 116. The device recited in claim 108 wherein the secondplurality of LTCC layers includes a ground shielding extending throughsaid layers to shield the MEMS capacitor or IC from radiating componentsin other layers.
 117. The device recited in claim 99 wherein the firstand second pluralities of LTCC layers include ground planes forshielding the first and second circuits.
 118. The device recited inclaim 101 wherein the buffer layer is a plurality of layers.
 119. Thedevice recited in claim 1 13 wherein the integrated circuits areflip-chip bonded to screen-printed surface metal patterns on a layer ofthe first plurality of LTCC layers.
 120. The device recited in claim 113wherein the integrated circuits are wire-bonded to screen-printedsurface metal patterns on a layer of the first plurality of LTCC layers.121. The device recited in claim 113 wherein the integrated circuits areflip-chip bonded to photo-patterned surface metal patterns on a layer ofthe first plurality of LTCC layers.
 122. The device recited in claim 113 wherein the integrated circuits are wire-bonded to photo-patternedsurface metal patterns on a layer of the first plurality of LTCC layers.123. The device recited in claim 113 wherein the integrated circuits areconnected to the variable capacitor so as to provide electrical controland closed-loop control of the variable capacitor value.
 124. Amicroelectromechanical variable capacitor device which operates at radiofrequencies compromising: a first substrate comprised of a firstplurality of low-temperature co-fired ceramic (“LTCC”) layers forming afirst circuit used in the operation of the device, and a secondsubstrate comprised of a second plurality of LTCC layers forming atleast a second circuit used in the operation of the device; and whereinthe second substrate is bonded to the first substrate so as to enclosethe MEMS variable capacitor device between the first and secondsubstrates.
 125. The MEMS device recited in claim 124 wherein the secondsubstrate is bonded to the first substrate to form a hermetically sealedchamber containing the MEMS variable capacitor device.
 126. The MEMSdevice recited in claim 124 wherein the first and second pluralities ofLTCC layers comprising the first and second substrates areinterconnected by vertical interconnects extending through the layers.127. The MEMS device recited in claim 124 wherein the first plurality ofLTCC layers comprising the first substrate includes a buffer layer thatserves as a substrate on which that the MEMS variable capacitor deviceis fabricated.
 128. The MEMS device recited in claim 124 wherein thevariable capacitor device employs electrostatic actuation to deflect themovable electrode and thereby change the capacitance of the device. 129.The MEMS device recited in claim 128 wherein the variable capacitordevice employs electrodes that are shaped so as to linearize the appliedelectrostatic voltage versus capacitance relationship of the device.130. The MEMS device recited in claim 124 wherein the variable capacitordevice employs mechanical barriers to stop the deflection of the movableelectrode at a predefined location and thereby set the tuning range ofthe device.
 131. The MEMS device recited in claim 124 wherein thevariable capacitor device uses non-linear springs so as to provide anon-linear mechanical restoring force to the movable electrode of thevariable capacitor whereby the non-linear spring compensates for thenon-linearity of the electrostatic actuation force.
 132. The MEMS devicerecited in claim 124 wherein the variable capacitor device employs atleast four electrodes so to provide for a two-port device and therebyde-couple the capacitance of the device from the actuation of saiddevice.
 133. The MEMS variable capacitor device recited in claim 124further comprising at least one integrated circuit bonded to the firstsubstrate.
 134. The MEMS variable capacitor device recited in claim 133wherein the first plurality of LTCC layers includes an interconnectlayer through which the at least one integrated circuit is connected tothe first substrate.
 135. The MEMS variable capacitor device recited inclaim 124 wherein the first plurality of LTCC layers includes aplurality of discrete components buried-in said layers.
 136. The MEMSvariable capacitor device recited in claim 135 wherein the firstplurality of buried-in discrete components contains at least onecomponent from the group consisting of is resistors, or capacitors andinductors.
 137. The MEMS variable capacitor device recited in claim 135wherein the first and second pluralities of LTCC layers include at leastone passive microwave device from the group consisting of transmissionlines, couplers and dividers.
 138. The MEMS variable capacitor devicerecited in claim 135 wherein the first plurality of LTCC layers includesa cavity in which the integrated circuits are bonded to the firstplurality of LTCC layers.
 139. The MEMS variable capacitor devicerecited in claim 135 wherein the integrated circuits include at leastone circuit from a group consisting of low-frequency analog/digital ICs,MMICS, and RFICs.
 140. The MEMS variable capacitor device recited inclaim 135 wherein the integrated circuits include at least one circuitfrom a group consisting of a control circuit for the MEMS variablecapacitor device, a power module for the MEMS variable capacitor device,a microprocessor.
 141. The MEMS variable capacitor device recited inclaim 135 wherein the second plurality of LTCC layers includes a groundshielding extending through said layers to shield the variable capacitorMEMS device or IC from radiating components in other layers.
 142. TheMEMS variable capacitor device recited in claim 135 wherein the firstand second pluralities of LTCC layers include ground planes forshielding the first and second circuits.
 143. The MEMS variablecapacitor device recited in claim 132 wherein the buffer layer is aplurality of layers.
 144. The MEMS variable capacitor device recited inclaim 134 wherein the integrated circuits are flip-chip bonded toscreen-printed surface metal patterns on a layer of the first pluralityof LTCC layers.
 145. The MEMS variable capacitor device recited in claim134 wherein the integrated circuits are wire-bonded to screen-printedsurface metal patterns on a layer of the first plurality of LTCC layers.146. The MEMS variable capacitor device recited in claim 136 wherein theintegrated circuits are flip-chip bonded to photo-patterned surfacemetal patterns on a layer of the first plurality of LTCC layers. 147.The MEMS variable capacitor device recited in claim 136 wherein theintegrated circuits are wire-bonded to photo-patterned surface metalpatterns on a layer of the first plurality of LTCC layers.
 148. The MEMSvariable capacitor device recited in claim 124 wherein the capacitanceof the device is adjusted by application of an electrical signal to saiddevice.
 149. The MEMS variable capacitor device recited in claim 148wherein the variable capacitor is actuated electrostatically.
 150. TheMEMS variable capacitor device recited in claim 148 wherein the variablecapacitor is electrostatically and zipper actuated so as to increase thetuning range of said MEMS variable capacitor device.
 151. The MEMSdevice recited in claim 150 wherein the variable capacitor deviceincludes electrodes that are shaped so as to linearize the appliedelectrostatic voltage versus capacitance relationship of the device.152. The MEMS device recited in claim 150 wherein the variable capacitordevice includes mechanical barriers to stop the deflection of themovable electrode at a predefined location and thereby set the tuningrange of the device.
 153. The MEMS device recited in claim 150 whereinthe variable capacitor device includes at least four electrodes so toprovide for a two-port device and thereby de-couples the capacitance ofthe device from the actuation of said device.
 154. The MEMS variablecapacitor device recited in claim 150 wherein the variable capacitorincludes mechanical stops that prevent shorting of the capacitorelectrodes.
 155. A microelectromechanical (MEMS) tunable inductor devicewhich operates at radio frequencies compromising: a first substratecomprised of a first plurality of low-temperature co-fired ceramic(“LTCC”) layers forming a first circuit used in the operation of thedevice, a second substrate comprised of a second plurality of LTCClayers forming at least a second circuit used in the operation of thedevice; a plurality of radio frequency (“RF”) microelectromechanicalswitches fabricated on the first substrate, a network of parallelinductors also fabricated on the first substrate, and wherein the secondsubstrate is bonded to the first substrate so as to enclose the RF MEMSswitches and inductors between the first and second substrates.
 156. TheMEMS device recited in claim 155 wherein the second substrate is bondedto the first substrate to form a hermetically sealed chamber containingthe plurality of MEMS switches and inductors.
 157. The MEMS devicerecited in claim 155 wherein the first and second pluralities of LTCClayers comprising the first and second substrates are interconnected byvertical interconnects extending through the layers.
 158. The MEMSdevice recited in claim 155 wherein the first plurality of LTCC layerscomprising the first substrate includes a buffer layer that serves as asubstrate on which a plurality of MEMS switches and inductors devicesare fabricated.
 159. The MEMS device recited in claim 155 wherein theplurality of MEMS switch devices are actuated by the application of anelectrostatic voltage to select the desired inductor in the network.160. A microelectromechanical systems (MEMS) tunable inductor-capacitornetwork device which operates at radio frequencies compromising: a firstsubstrate comprised of a first plurality of low-temperature co-firedceramic (“LTCC”) layers forming a first circuit used in the operation ofthe device or system, a second substrate comprised of a second pluralityof LTCC layers forming at least a second circuit used in the operationof the device, a plurality of RF microelectromechanical switchesfabricated on the first substrate, a network of parallel inductordevices formed on the first substrate, and at least one variablecapacitor device formed on the first substrate, wherein the secondsubstrate is bonded to the first substrate so as to enclose the at leastone MEMS switches and inductor and capacitor devices between the firstand second substrates.
 161. The MEMS device recited in claim 160 whereinthe second substrate is bonded to the first substrate to form ahermetically sealed chamber containing the plurality of MEMS switchesand MEMS variable capacitors.
 162. The MEMS device recited in claim 160wherein the first and second pluralities of LTCC layers comprising thefirst and second substrates are interconnected by vertical interconnectsextending through the layers.
 163. The MEMS device recited in claim 160wherein the first plurality of LTCC layers comprising the firstsubstrate includes a buffer layer that serves as a substrate on which aplurality of MEMS switches and inductors devices are fabricated. 164.The MEMS device recited in claim 160 wherein the plurality of MEMSswitch devices employ electrostatic actuation to select the desiredinductor in the network.
 165. The MEMS device recited in claim 160wherein the plurality of MEMS variable capacitor devices employelectrostatic actuation to select the desired inductor in the network166. The MEMS device recited in claim 160 wherein the tunableinductor-capacitor network is used a tunable filter.
 167. A phased arrayantenna system comprising: a plurality of sub-array modules integratedtogether to form the phased array antenna, and at least one amplifierconnected to the plurality of sub-array modules, each of the sub-arraymodules being comprised of a plurality of radiating elements, each ofthe radiating elements including: a first module comprised of a firstplurality of low-temperature co-fired ceramic (“LTCC”) layers forming atleast one first circuit used in the operation of the phased arrayantenna; a second module comprised of a second plurality of LTCC layersforming at least a second circuit used in the operation of thephased-array antenna; at least one radiating patch formed on the secondmodule; and at least one phase shifter fabricated from at least onemicroelectromechanical (“MEMS”) switch and formed between the first andsecond modules; and wherein the second module is bonded to the firstmodule so as to enclose the at least one MEMS phase shifter between thefirst and second modules.
 168. The phased array antenna system recitedin claim 167 wherein the second module is bonded to the first module toform a hermetically sealed chamber containing the at least one MEMSphase shifter.
 169. The phased array antenna system recited in claim 167wherein the first and second pluralities of LTCC layers areinterconnected by vertical interconnects extending through the layers.170. The phased array antenna system recited in claim 167 wherein the atleast one second circuit formed in the second plurality of LTCC layersis a polarizer circuit.
 171. The phased array antenna system recited inclaim 167 wherein the at least one first circuit formed in the firstplurality of LTCC layers is a plurality of circuits including a powerdivider circuit and a band pass filter circuit.
 172. The phased arrayantenna system recited in claim 167 wherein the first plurality of LTCClayers includes a buffer layer that serves as a substrate on which theat least one MEMS phase shifter is fabricated.
 173. The phased arrayantenna system recited in claim 167 further comprising at least oneintegrated circuit bonded to the first module.
 174. The phased arrayantenna system recited in claim 173 wherein the first plurality of LTCClayers includes an interconnect layer through which the at least oneintegrated circuit is connected to the first module.
 175. The phasedarray antenna system recited in claim 167 wherein the system includes aplurality of amplifiers, each of the amplifiers being connected to acorresponding one of the plurality of sub-array modules.
 176. The phasedarray antenna system recited in claim 167 wherein each of the radiatingelements includes a plurality of radiating patches and a correspondingplurality of MEMS phase shifters.
 177. The phased array antenna systemrecited in claim 167 wherein the first plurality of LTCC layers includesa plurality of discrete components buried-in said layers.
 178. Thephased array antenna system recited in claim 177 wherein the pluralityof buried-in discrete components is resistors, capacitors, and/orinductors.
 179. The phased array antenna system recited in claim 167wherein the first and second pluralities of LTCC layers include at leastone passive microwave device selected from the group consisting oftransmission lines, couplers, and dividers.
 180. The phased arrayantenna system recited in claim 173 wherein the first plurality of LTCClayers includes a cavity in which the integrated circuits are bonded tothe first array antenna.
 181. The phased array antenna system recited inclaim 173 wherein the integrated circuits include at least one circuitselected from a group consisting of low-frequency analog/digital ICs,MMICs, and RFICs.
 182. The phased array antenna system recited in claim173 wherein the integrated circuits include at least one circuit from agroup consisting of a control circuit for the MEMS phase shifter, apower module for the MEMS phase shifter, a microprocessor, a signalprocessor, a high frequency power amplifier, a high frequency low noiseamplifier, high frequency down or up converters.
 183. The phased arrayantenna system recited in claim 167 wherein the second plurality of LTCClayers includes ground shielding extending through said layers to shieldthe at least one radiating element from radiating elements in otherphase antennas.
 184. The phased array antenna system recited in claim167 wherein the first and second pluralities of LTCC layers includeground planes for shielding the first and second circuits.
 185. Thephased array antenna system recited in claim 172 wherein the bufferlayer is a plurality of layers.
 186. The phased array antenna systemrecited in claim 173 wherein the integrated circuits are flip-chipbonded to screen-printed surface metal patterns on a layer of the firstplurality of LTCC layers.
 187. The phased array antenna system recitedin claim 173 wherein the integrated circuits are wire-bonded toscreen-printed surface metal patterns on a layer of the first pluralityof LTCC layers.
 188. The phased array antenna system recited in claim173 wherein the integrated circuits are flip-chip bonded tophoto-patterned surface metal patterns on a layer of the first pluralityof LTCC layers.
 189. The phased array antenna system recited in claim173 wherein the integrated circuits are wire-bonded to photo-patternedsurface metal patterns on a layer of the first plurality of LTCC layers.190. The phased array antenna system recited in claim 167 wherein thesecond plurality of LTCC layers includes a plurality of radiation layerson which is fabricated the at least one radiating element.
 191. A phasedarray antenna system comprising: a plurality of low-temperature co-firedceramic (“LTCC”) modules integrated together, and at least one amplifierconnected to the plurality of LTCC modules, each LTCC module being aradiating element and being comprised of: a first plurality of LTCClayers forming at least one first circuit used in the operation of thephased array antenna; a second plurality of LTCC layers forming at leasta second circuit used in the operation of the phased-array antenna; atleast one microelectromechanical (“MEMS”) device formed between thefirst and second pluralities of LTCC layers, the second plurality ofLTCC layers being bonded to the first plurality of LTCC layers wherebythe at least one MEMS device is enclosed between the first and secondpluralities of LTCC layers; and at least one radiating patch formed onthe second plurality of LTCC layers.
 192. The phased array antennasystem recited in claim 191 wherein the second plurality of LTCC layersis bonded to the first plurality of LTCC layers to form a hermeticallysealed chamber containing the at least one MEMS device.
 193. The phasedarray antenna system recited in claim 191 wherein the first plurality ofLTCC layers includes a buffer layer that serves as a substrate on whichthe at least one MEMS device is fabricated.
 194. The phased arrayantenna system recited in claim 191 further comprising at least oneintegrated circuit bonded to the first plurality of LTCC layers. 195.The phased array antenna system recited in claim 194 further comprisinga plurality of integrated circuits including at least one circuit from agroup consisting of low-frequency analog/digital ICs, MMICs, and RFICs.196. The phased array antenna system recited in claim 194 furthercomprising a plurality of integrated circuits including at least onecircuit from a group consisting of a control circuit for the MEMSdevice, a power module for the MEMS device, a microprocessor, a signalprocessor, a high frequency power amplifier, a high frequency low noiseamplifier, high frequency down-converters.
 197. An array antennacomprising: a first ceramic module formed from of a first plurality ofdielectric layers, the first plurality of dielectric layers including atleast one first circuit layer; a second ceramic module formed from of asecond plurality of dielectric layers, the second plurality ofdielectric layers including at least one second circuit layer, a layerbetween the first and second ceramic modules including at least onemicroelectromechanical switch (“MEMS”) forming at least onephase-shifter, a second ceramic module being bonded to the first ceramicmodule and thereby forming a cavity on top of the MEMS switch.
 198. Thearray antenna of claim 197, wherein the ceramic modules are formed usingan LTCC process.
 199. The array antenna of claim 197, wherein theceramic modules are formed using an HTCC process.
 200. An array antennacomprising: a first ceramic module formed from of a first plurality ofdielectric layers, the first plurality of dielectric layers including atleast one first circuit layer, a buffer layer, and a plurality ofinterconnections between the at least one first circuit layer and thebuffer layer; a second ceramic module formed from of a second pluralityof dielectric layers, the second plurality of dielectric layersincluding at least one second circuit layer, a cover layer, a pluralityof radiation layers, and a plurality of interconnections between thesecond circuit layer, cover layer, and radiation layers; and a layerbetween the first and second ceramic modules including at least onemicroelectromechanical switch (“MEMS”) forming at least onephase-shifter.
 201. The array antenna of claim 200 further comprising aplurality of integrated circuits mounted on the first ceramic module,the first plurality of dielectric layers further includinginterconnecting layers for connecting the integrated circuits to thedielectric layers forming the first and second ceramic modules.
 202. Thearray antenna of claim 200, wherein the ceramic modules are formed usingan LTCC process.
 203. The array antenna of claim 200, wherein theceramic modules are formed using an HTCC process.
 204. A method offorming a radiating element for an array antenna comprising the stepsof: fabricating a first module from a first plurality of low-temperatureco-fired ceramic (“LTCC”) layers, the first plurality of layers formingat least a first circuit used in the operation of the array antenna;fabricating a second module from a second plurality of low-temperatureco-fired ceramic (“LTCC”) layers, the second plurality of layers formingat least a second circuit used in the operation of the array antenna;polishing a surface of a front layer of the first module to be used as asubstrate after fabrication of the first module is completed;fabricating on the front layer at least one microelectromechanicalswitch (“MEMS”) using MEMS processing; and bonding the first and secondmodules together to thereby form a cavity containing the at least oneMEMS switch.
 205. The method of forming a radiating element for an arrayantenna as recited in claim 204 further comprising the steps ofpolishing a surface of a back layer of the second module to be used as acover after fabrication of the second module is completed and applyingtwo-component brazing materials on the front and back layers prior tobonding the first and second modules together.
 206. The method offorming a radiating element for an array antenna as recited in claim 204wherein the step of bonding the first and second modules together isperformed using eutectic bonding.
 207. The method of forming a radiatingelement for an array antenna as recited in claim 204 wherein the step ofbonding the first and second modules together is performed using aninsulating layer such as glass-frit.
 208. The method of forming aradiating element for an array antenna as recited in claim 204 whereinthe step of bonding the first and second modules together is performedusing an insulating layers such as a thermalsetting polyimide film. 209.The method of forming a radiating element for an array antenna asrecited in claim 204 wherein the step of applying two-component brazingmaterials on the front and back layers comprises the steps of:depositing a plurality of first contact pads on a front layer of thefirst module; planarizing the front layer of the first module;depositing an adhesion layer and a soldering conductor on the firstcontact pads; firing the first module at a temperature greater than 800°C.; depositing a plurality of second contact pads on a back layer of thesecond module; planarizing the back layer of the second module;(optional) depositing an adhesion layer and a soldering conductor on thesecond contact pads; and firing the first module at a temperaturegreater than 800° C.
 210. The method of forming a radiating element foran array antenna as recited in claim 204 wherein the step of polishingthe surfaces of the front and back layers is performed using amechanical or chemical/mechanical polish.
 211. The method of forming aradiating element for an array antenna as recited in claim 205 whereinthe step of polishing the surfaces of the front and back layers isperformed using a mechanical or chemical/mechanical polish.
 212. Themethod of forming a radiating element for an array antenna as recited inclaim 204 wherein the step of bonding the first and second modulestogether is performed at low pressure and in a low-humidity environment.213. The method of forming a radiating element for an array antenna asrecited in claim 204 wherein the step of bonding the first and secondmodules together is performed in an inert gas atmosphere.
 214. Themethod of forming a radiating element for an array antenna as recited inclaim 204 wherein the first and second modules are bonded together tothereby form a hermetically sealed cavity containing the at least oneMEMS switch.
 215. The method of forming a radiating element for an arrayantenna as recited in claim 204 wherein the MEMS switch is a phaseshifter.
 216. The method of forming a radiating element for an arrayantenna as recited in claim 204 further comprising the step of formingvertical interconnects extending through the first and secondpluralities of LTCC layers.
 217. The method of forming a radiatingelement for an array antenna as recited in claim 204 further comprisingthe step of forming a polarizer circuit in the second plurality of LTCClayers.
 218. The method of forming a radiating element for an arrayantenna as recited in claim 204 further comprising the step of forming apower divider circuit and a band pass filter circuit in the firstplurality of LTCC layers.
 219. The method of forming a radiating elementfor an array antenna as recited in claim 204 further comprising the stepof forming in the first plurality of LTCC layers a buffer layer that isa substrate on which the at least one MEMS phase shifter is fabricated.210. The method of forming a radiating element for an array antenna asrecited in claim 204 further comprising the step of bonding to one ofthe first plurality of LTCC layers at least one integrated circuit. 211.The method of forming a radiating element for an array antenna asrecited in claim 210 further comprising the step of forming in the firstplurality of LTCC layers an interconnect layer for interconnecting theintegrated circuit to the array antenna.
 212. The method of forming aradiating element for an array antenna as recited in claim 204 furthercomprising the step of forming in the second plurality of LTCC layers aplurality of radiating layers with at least one radiating patchfabricated on one of the radiating layers.
 213. The method of forming aradiating element for an array antenna as recited in claim 204 furthercomprising the step of fabricating in the first plurality of LTCC layersa plurality of buried-in discrete components.
 214. The method of forminga radiating element for an array antenna as recited in claim 213 whereinthe discrete components are resistors, capacitors, and/or inductors.215. The method of forming a radiating element for an array antenna asrecited in claim 204 further comprising the step of forming in the firstand second pluralities of LTCC layers screen-printed buried metalpatterns that are used to define interconnections and passive microwavedevices.
 216. The method of forming a radiating element for an arrayantenna as recited in claim 215 wherein the passive microwave devicesinclude at least one device from the group consisting of transmissionlines, couplers, and dividers.
 217. The method of forming a radiatingelement for an array antenna as recited in claim 204 further comprisingthe step of forming in the first and second pluralities of LTCC layersphoto-patterned buried metal patterns that are used to defineinterconnections and passive microwave devices.
 218. The method offorming a radiating element for an array antenna as recited in claim 217wherein the passive microwave devices include at least one device fromthe group consisting of transmission lines, couplers, and dividers. 219.The method of forming a radiating element for an array antenna asrecited in claim 212 further comprising the step of forming in thesecond plurality of LTCC layers ground shielding extending through saidlayers to shield the at least one radiating patch from radiating patchesin other array antennas.
 220. The method of forming a radiating elementfor an array antenna as recited in claim 211 further comprising the stepof flip-chip bonding the integrated circuits to screen-printed surfacemetal patterns on a layer of the first plurality of LTCC layers. 221.The method of forming a radiating element for an array antenna asrecited in claim 211 further comprising the step of wire-bonding theintegrated circuits to screen-printed surface metal patterns on a layerof the first plurality of LTCC layers.
 222. The method of forming aradiating element for an array antenna as recited in claim 211 furthercomprising the step of flip-chip bonding the integrated circuits tophoto-patterned surface metal patterns on a layer of the first pluralityof LTCC layers.
 223. The method of forming a radiating element for anarray antenna as recited in claim 211 further comprising the step ofwire-bonding the integrated circuits to photo-patterned surface metalpatterns on a layer of the first plurality of LTCC layers.
 224. Themethod of forming a radiating element for an array antenna as recited inclaim 204 wherein the MEMS process is performed in large-area-processingtools or standard semiconductor tools.
 225. A method of forming an arrayantenna comprising the steps of: fabricating a plurality of radiatingelements, each of the radiating elements being fabricated by forming atleast one microelectromechanical (“MEMS”) switch on a firstlow-temperature co-fired ceramic (“LTCC”) module, and bonding a secondLTCC bonded to the first LTCC module, whereby the MEMS switch is locatedin a cavity between the first and second LTCC modules; forming aplurality of sub-array modules, each of the sub-array modules beingformed from a plurality of radiating elements; integrating the pluralityof sub-array modules together to form the phased array antenna; andconnecting the plurality of sub-array modules to at least one amplifier.226. A method of forming an electrical device comprising the steps of:fabricating a first module from a first plurality of low-temperatureco-fired ceramic (“LTCC”) layers, the first plurality of layers formingat least a first circuit used in the operation of the electrical device;fabricating a second module from a second plurality of low-temperatureco-fired ceramic (“LTCC”) layers, the second plurality of layers formingat least a second circuit used in the operation of the electricaldevice; polishing a surface of a front layer of the first module to beused as a substrate after fabrication of the first module is completed;fabricating on the front layer at least one microelectromechanicaldevice (“MEMS”) using standard MEMS processing; and bonding the firstand second modules together to thereby form a cavity containing the atleast one MEMS device.
 227. The method of forming an array antenna asrecited in claim 226 further comprising the steps of polishing a surfaceof a back layer of the second module to be used as a cover afterfabrication of the second module is completed and applying two-componentbrazing materials on the front and back layers prior to bonding thefirst and second modules together.
 228. The method of forming an arrayantenna as recited in claim 226 wherein the step of bonding the firstand second modules together is performed using eutectic bonding. 229.The method of forming an array antenna as recited in claim 226 whereinthe step of bonding the first and second modules together is performedusing an insulating layer such as glass-frit.
 230. The method of formingan array antenna as recited in claim 226 wherein the step of bonding thefirst and second modules together is performed using an insulatinglayers such as a thermal setting polyimide film.
 231. The method offorming an electrical device as recited in claim 226 wherein the step ofapplying two-component brazing materials on the front and back layerscomprises the steps of: depositing a plurality of first contact pads ona front layer of the first module; planarizing the front layer of thefirst module; depositing an adhesion layer and a soldering conductor onthe first contact pads; firing the first module at a temperature greaterthan 800° C.; depositing a plurality of second contact pads on a backlayer of the second module; planarizing the back layer of the secondmodule; depositing an adhesion layer and a soldering conductor on thesecond contact pads; and firing the first module at a temperaturegreater than 800° C.
 232. The method of forming an electrical device asrecited in claim 226 wherein the step of polishing surfaces of the frontand back layers is performed using a mechanical or chemical/mechanicalpolish.
 233. The method of forming an electrical device as recited inclaim 226 wherein the step of bonding the first and second modulestogether is performed at low pressure and in a low-humidity environment.234. The method of forming an electrical device as recited in claim 226wherein the first and second modules are bonded together to thereby forma hermetically sealed cavity containing the at least one MEMS device.235. The method of forming an electrical device as recited in claim 226further comprising the step of forming vertical interconnects extendingthrough the first and second pluralities of LTCC layers.
 236. The methodof forming an electrical device as recited in claim 226 furthercomprising the step of bonding to one of the first plurality of LTCClayers at least one integrated circuit.
 237. The method of forming anelectrical device as recited in claim 236 further comprising the step offorming in the first plurality of LTCC layers an interconnect layer forinterconnecting the integrated circuit to the electrical device. 238.The method of forming an electrical device as recited in claim 226further comprising the step of fabricating in the first plurality ofLTCC layers a plurality of buried-in discrete components.
 239. Themethod of forming an electrical device as recited in claim 235 whereinthe vertical interconnects are metal-filled vias.
 240. The method offorming an electrical device as recited in claim 226 wherein the MEMSprocess is performed in large-area-processing tools or standardsemiconductor tools.
 241. The method of forming a radiating element foran array antenna as recited in claim 209 wherein the step of polishingthe surfaces of the front and back layers is performed using aselectively protective and removable layer on exposed metal duringpolishing to prevent or reduce dishing.
 242. The method of forming aradiating element for an array antenna as recited in claim 218 whereinthe at least one MEMS switch contained in the hermetically sealed cavityis coated with a surface treatment to prevent stiction.
 243. The methodof forming a radiating element for an array antenna as recited in claim242 wherein the at least one MEMS switch is coated with a surfacetreatment selected from the group consisting of dichlorodimethylsilane(DDMS) monolayer and octadecyltrichlorosilane (OTS) self-assembledmonolayer.
 244. The method of forming a radiating element for an arrayantenna as recited in claim 204 wherein the at least one MEMS switch issealed with a surface treatment to prevent stiction.
 245. The method offorming a radiating element for an array antenna as recited in claim 204wherein the at least one MEMS switch is sealed with a surface treatmentto prevent stiction and maintain low-resistance contacts in the at leastone MEMS switch by avoiding contamination and unwanted chemicalreactions, such as oxidation.
 246. The method of forming a radiatingelement for an array antenna as recited in claim 244 wherein the atleast one MEMS switch is sealed with a surface treatment selected fromthe group consisting of dichlorodimethylsilane (DDMS) monolayer andoctadecyltrichlorosilane (OTS) self-assembled monolayer.
 247. The methodof forming a radiating element for an array antenna as recited in claim244 wherein the at least one MEMS switch is sealed with a product thatcan be used on metal surfaces to minimize unintentional adhesion inmechanical switches or other contacting or near-contacting surfaces.247. A phased array antenna system comprising: a plurality of sub-arraymodules formed on a low-temperature co-fired ceramic (“LTCC”) wafer, andat least one amplifier connected to the plurality of sub-array modules,each of the sub-array modules being comprised of a plurality ofradiating elements, each of the radiating elements including: a firstmodule comprised of a first plurality of LTCC layers forming at leastone first circuit used in the operation of the phased array antenna; asecond module comprised of a second plurality of LTCC layers forming atleast a second circuit used in the operation of the phased-arrayantenna; at least one radiating patch formed on the second module; andat least one phase shifter fabricated from at least onemicroelectromechanical (“MEMS”) switch and formed between the first andsecond modules; and wherein the second module is bonded to the firstmodule so as to enclose the at least one MEMS phase shifter between thefirst and second modules.
 249. A phased array antenna system comprising:a plurality of sub-array modules integrated together to form the phasedarray antenna, each of the sub-array modules being comprised of aplurality of radiating elements, each of the radiating elementsincluding: a first module comprised of a first plurality oflow-temperature co-fired ceramic (“LTCC”) layers forming at least onefirst circuit used in the operation of the phased array antenna; asecond module comprised of a second plurality of LTCC layers forming atleast a second circuit used in the operation of the phased-arrayantenna; at least one radiating patch and at least one amplifierconnected to the radiating patch formed on the second module; and atleast one phase shifter fabricated from at least onemicroelectromechanical (“MEMS”) switch and formed between the first andsecond modules; and wherein the second module is bonded to the firstmodule so as to enclose the at least one MEMS phase shifter between thefirst and second modules.
 250. A phased array antenna system comprising:a plurality of sub-array modules integrated together to form the phasedarray antenna, and at least one amplifier connected to the plurality ofsub-array modules, each of the sub-array modules being comprised of aplurality of radiating elements, each of the radiating elementsincluding: at least a first module comprised of a first plurality oflow-temperature co-fired ceramic (“LTCC”) layers forming at least onefirst circuit used in the operation of the phased array antenna; atleast a second module comprised of a second plurality of LTCC layersforming at least a second circuit used in the operation of thephased-array antenna; at least one radiating patch formed on the secondmodule; and at least one phase shifter fabricated from at least onemicroelectromechanical (“MEMS”) switch and formed between the first andsecond modules; and wherein the second module is bonded to the firstmodule so as to enclose the at least one MEMS phase shifter between thefirst and second modules.
 251. A radio frequency system compromising: aplurality of modules formed on a low-temperature co-fired ceramic(“LTCC”) wafer, each of the modules including: at least onemicroelectromechanical (“MEMS”) device, at least a first plurality ofLTCC layers forming at least one first circuit used in the operation ofthe MEMS device, and at least a second plurality of LTCC layers formingat least one second circuit used in the operation of the MEMS device,Wherein the MEMS device is formed between the first and secondpluralities of LTCC layers, the second plurality of LTCC layers beingbonded to the first plurality of LTCC layers whereby the MEMS device isenclosed between the first and second pluralities of LTCC layers. 252.The MEMS device of claim 32, wherein the ceramic modules are formed from943 Green Tape™.
 253. The MEMS device of claim 32, wherein the ceramicmodules are formed from 951 Green Tape™.
 254. The MEMS device of claim42, wherein the ceramic modules are formed from 943 Green Tape™. 255.The MEMS device of claim 42, wherein the ceramic modules are formed from951 Green Tape™.
 256. The MEMS device of claim 198, wherein the ceramicmodules are formed from 943 Green Tape™.
 257. The MEMS device of claim198, wherein the ceramic modules are formed from 951 Green Tape™. 258.The MEMS device of claim 202, wherein the ceramic modules are formedfrom 943 Green Tape™.
 259. The MEMS device of claim 202, wherein theceramic modules are formed from 951 Green Tape™.